Section III Table of Contents

SECTION IV: Service Practices

Basic Vapor-Compression A/C Principles

It is not the intent of this section to teach basic air-conditioner theory; however, a simple discussion of the basic cycle is useful for describing the effects of non-condensable gases, moisture, and contaminates on the air-conditioning system.

The most basic vapor-compression air conditioning system consists of four major components: compressor, evaporator, condenser, and expansion device. As every technician knows, actual practical hardware contains many other critical components for reliable, trouble-free operation, such as a control system, high-pressure and low-pressure safety controls, liquid receiver, accumulator, oil separator, etc. However, the four basic components are all that is needed to illustrate the point of this section.

Refrigerant adsorbs energy, (provides cooling), as it is evaporated, that is, as it boils and turns from liquid to vapor. For pure refrigerants, if the refrigerant evaporates at a constant pressure, then the evaporation occurs at a constant temperature while both liquid and vapor are present. Likewise, refrigerant rejects energy, (gives off heat), as it condenses from vapor to liquid. For pure refrigerants and azeotropic mixtures, if the condensation occurs at a constant pressure, then the condensation will occur at a constant temperature until all the vapor has condensed to a liquid. Therefore, for evaporation, or condensation, the temperature and pressure are related by the pressure/temperature saturation curve. Table 4 presents saturation temperature/pressure data for CFC-12, and HFC-134a.

If a technician has an unknown refrigerant in a recovery cylinder, and both liquid and vapor are present in the recovery cylinder, then he/she can verify the refrigerant type by comparing the pressure and temperature with the saturation pressure temperatures curves for the various refrigerants. Unfortunately, the temperature pressure relationship of R-12 and R-134a, are too close to distinguish. For example, suppose the unknown refrigerant has a tank temperature of 80°F. If the refrigerant is HFC-134a, then the tank pressure would be 86 psig, (referring to Table 4), and if the refrigerant was CFC-12, the tank pressure would be 84 psig, because of gauge inaccuracy and non-condensable gas effects this is too close to call. However, accurate refrigerant gas analyzers are commercially available to determine refrigerant types and to verify that there is no refrigerant contamination during a refrigerant change-over.

A brief discussion of the operating vapor-compression cycle is helpful to indicate other potential air-conditioning problems in real systems. In the basic cycle, slightly subcooled refrigerant leaves the condenser at high pressure, and the pressure is dropped via the throttling device, (capillary tube, TXV, etc.), before it enters the evaporator. It enters the evaporator as two-phase mixture (liquid and vapor) and evaporates or boils at low temperature, adsorbing heat. Slightly superheated refrigerant vapor, exits the evaporator and enters the compressor where the pressure and temperature are increased as the compressor, compresses the refrigerant vapor. The vapor, leaving the compressor, is superheated, and the compressor discharge is the hottest point in the cycle. This refrigerant is cooled and condensed in the condenser where heat is rejected and the refrigerant is condensed to liquid. Refrigerant actually leaves the condenser slightly subcooled to assure condensation has been complete. Any non-condensable vapors in the system will be unable to condense in the condenser and will appear as gas bubbles in the condensed liquid stream. These non-condensables may collect in the condenser and displace refrigerant from the condenser heat exchanger, thereby reducing the effective surface area of the condenser.

Any water in the system will most likely freeze in the expansion valve, because this is the point where refrigerant is cooled by the evaporation occurring as a result of the sudden pressure drop, and the expansion device also represents the smallest passage way in the overall system. It is this reason why filter-driers are typically located just upstream of the expansion device.

Table 4. Pressure/Temperature Saturation Relationship for Common Refrigerants

Leak Testing

Automotive systems naturally leak small amounts of refrigerant. This slow leakage comes from the inherent minor permeability of the soft, flexible hoses in the system, and the shaft seal on the compressor. Another possible source of leaks are at the threaded connections for the hoses, the gasketed face seals and any location where the soft, flexible hoses are crimped and join harder metal tubing. It is not an EPA requirement to repair a leak prior to recharging a motor vehicle air conditioning system, but it is highly recommended! Some states do have state laws requiring leak repairs. (Note: states can impose laws which are more strict than federal laws.) In addition, EPA does not require that the refrigerant be recovered and cleaned prior to recharging the system with additional refrigerant, that is you can legally top off A/C systems. However, some replacement refrigerant blends, can not be topped-off for thermodynamic reasons. When there is a leak in a system with a non-azeotropic refrigerant blend the more volatile refrigerants leak more than the other refrigerants in the blend. This changes the proportions of the blend and alters the blend's properties. For these non-azeotropic blends the refrigerant must be recovered and replaced, rather than topped off. This is a significant drawback of these non-azeotropic blends. Both R-134a and R-12 are pure refrigerants and can therefore be topped off, in addition, azeotropic blends, behave as a pure refrigerant and can also be topped off.

A service technician's major responsibility is to minimize the amount of refrigerant that escapes into the atmosphere. One of the worst things a service technician can do is service an automotive air conditioning system and then find out that the system has large leaks.

It is a good idea to give the vehicle a thorough visual inspection before starting any service procedures. Look at the entire refrigerant circuit while watching for signs of oil leakage, corroded or damaged lines, hoses, or other components. Look for uncapped Schrader valves, dust caps, or missing and/or damaged O-rings. Topping off a system that leaks refrigerant, lets harmful refrigerants escape into the atmosphere.

A vacuum test is not the best method of leak testing a system. This method allows air, and thus moisture, to enter the system, and the technician cannot determine from the vacuum where the leak is, but only that there is a leak. Also, when a vacuum is used for leak checking, it is only proving that the system will not leak under a pressure difference of 14.7 psi. (If all of the atmosphere is removed from a system, there is only the atmosphere's pressure trying to get back into the system, therefore a 14.7 psi pressure difference.)

When checking for a leak using a vacuum, the technician is using a reverse pressure, (the atmosphere trying to get into the system), of only 14.7 psi; however, under normal operating conditions, the system may be operating under a pressure of more than a hundred psig, that is, many times the vacuum pressure difference. Always leak check with dry nitrogen to a pressure of approximately 130 psig, and never more than 150 psig.

Some leaks are simply not visible to the technician. In this case, leak detection devices must be used. SAE document J1628, provides guidelines for the use of such devices. Always locate and fix the leak before adding the proper refrigerant charge. Only the refrigerant that is specified for the system should be used for leak checking. This prevents any chemical contamination from one refrigerant to another.

Never use pure oxygen or air for leak checking. Air contains 18 percent oxygen, which when mixed with many refrigerants, (as would be done in a leak checking procedure), could cause an explosion if a flame is encountered. The pure oxygen and/or the oxygen in the air can combine with the refrigerant or oil and make an explosive mixture. Pure oxygen and oxygen in the air will oxidize system oil, very rapidly. In a closed system, pressure from the oxidizing oil can build up rapidly and may generate pressures to a point of exploding. The use of air for leak checking will also introduce a tremendous amount of moisture into the system. Typical ambient air can contain thousands of PPM (Parts Per Million) of moisture.

NOTE: Contained, recovered or recycled liquid refrigerant, contaminated with a small amount of air, does not constitute a flammability hazard. Use, however, of refrigerant contaminated with air will result in abnormally high operating system pressures, excess superheat, and possible major system damage. Use the Non-Condensable Gas Determination and Removal method described later in this section to determine if non-condensable gases are present and to remove these non-condensables.

If the system's refrigerant is to be used for leak checking, at least 50 psig of pressure is needed in both high and low sides of the system for leak checking. This means that the system does not have to be fully charged to leak check; also, leak checking should be done with the engine off. Even though a minimum of 50 psig is required for leak checking, it is not enough refrigerant to determine if the system will produce useful cooling. If the compressor is to be operated, refrigerant will have to be added to the system so the service technician can systematically troubleshoot and detect problems.

Refrigerant that is used for leak checking must be recovered and cannot be released into the atmosphere. To knowingly release refrigerant into the atmosphere is a violation of the Clean Air Act with fines up to $27,500 per occurrence.

No one method, should be relied upon to detect refrigerant leaks. Electronic leak detectors are designed to find leaks of just fractions of an ounce per year. Some electronic detectors can detect both R-12 and R-134a, where others detect only one refrigerant. R-134a has no chlorine in its molecule and is harder to detect. The leak detector has to have a higher sensitivity to detect the more elusive fluorine molecule in R-134a. When purchasing a leak detector for mobile air conditioning service, make sure it will find the refrigerant you are trying to detect. The more modern leak devices can detect both R-12 and R-134a refrigerants. SAE document J1628, should be used by mobile air conditioning service technicians when leak checking any vehicle. This document explains the use of a certified electronic leak detector according to SAE J1627 specifications. Some leaks are very hard to find. In fact, a service technician will often finish checking a vehicle and find that there are no detectable leaks. However, just because the technician didn't find any leaks doesn't mean that the system doesn't leak. Some leaks are vibration dependent, temperature dependent, pressure dependent, or a combination of the three. This is why it is important to practice good service procedures and workmanship. Always double check the system before closing the hood.

Leak Repairs

Once a leak is discovered, common sense will typically dictate the proper repair method. If a rubber hose is leaking it must be replaced. The entire plumbing assembly can be replaced or the rubber hose can be replaced. Never reuse a leaking hose. Likewise, leaking fittings can be tightened, however if that does not repair the leak, then the o-ring or face seal must be replaced. Use a small drop of compressor lubricant on the o-ring or face seal before reassembly. If a compressor shaft seal is leaking the compressor must be replaced or rebuilt.

Some aftermarket products are sold that claim to seal leaks by reacting inside the system at the source of the leak and plugging the leak (by forming a solid reside). In addition, some products are sold as "O-ring sealants" that are claimed to cause O-rings to swell to stop leaks. Avoid all such products. It is never a good idea to add any foreign substance into an air conditioning system due to potential unforeseen chemical incompatibilities with the lubricant, refrigerant or materials of construction. Furthermore, the introduction of a chemical that is specifically designed to form a solid residue, (to plug a leak), is an especially bad idea. They will also invalidate a manufacturers warranty. If tubing assemblies, or heat exchangers are leaking they must be replaced.

System Flushing

Today, the Clean Air Act prohibits the use of CFCs and/or methylchloroform in any flushing procedure in which the flushing agent is vented to the atmosphere. R-11 and R-113 have been used successfully for many years in flushing out mobile air conditioning systems. These refrigerants are CFCs, and are no longer produced. Also residual chlorine from any CFC, (including R-11, R-12, or R-113), left in the air conditioning system will cause serious chemical stability problems in R-134a systems. Use of any flushing fluid, other than the refrigerant prescribed for the MVAC system is not recommended.

There are some solvents on the market supposedly designed for system flushing. However, there is a question as to whether these solvents will vaporize and come out of the system when a deep vacuum is pulled on it. If residual solvents remain in the active air conditioning system, the chemical stability of the refrigerant and oil may be affected. This is why some mobile air conditioning manufacturers recommend not flushing after a mechanical failure. Because of chemical stability and potential moisture related problems, Mainstream does not recommend the use of any cleaning or flushing fluid other than Qwik System Flush™ for MVAC systems. Qwik System Flush has been shown (in independent third-party laboratory tests) to effectively flush acid, oil, water and other impurities without leaving any residue.

Filter-Driers

Using a filter-drier, just before the expansion valve or orifice tube, has proven to be a more effective method for catching particle residue, moisture, and debris from failed parts and/or components. There are in-line filters designed to catch the harmful particles and still not restrict the vehicle's air conditioning system.

Refrigerant Blends and System Retrofitting

To provide a historical perspective into replacement refrigerants, all CFC refrigerants, including CFC-12  were banned in the USA, because of their ozone depletion potential. For new MVAC applications, CFC-12 was replaced by HFC-134a. There are also many HFC blends that have been sold by aftermarket suppliers for the replacement of CFC-12 and HFC-134a. In addition, new vehicle manufacturer's and the MVAC industry have been investigating improved refrigerants to potentially replace HFC-134a because of its high global warming potential.

Refrigerant blends are mixtures of refrigerant that have been formulated to provide a similar pressure/temperature relationship to the original refrigerant. Blends can be HCFC based, HFC based, or a combination of both. The HCFC-based blends are only interim CFC replacements because of their non-zero ODP. The HFC-based blends will be the long-term replacements for certain CFCs and HCFCs until researchers can find single refrigerants to replace them or until stricter GWP legislation forces refrigerants with lower GWP.

Many blends also use a flammable component (such as propane, or butane) as one of the components in the blend. Table 5 contains a list of common refrigerant blends, which have at least one flammable component, and are available on the market for stationary HVAC applications. Not all of these refrigerant blends have Significant New Alternatives Policy (SNAP) approval for use in automotive applications. Table 6 contains a list of the Motor Vehicle Air Conditioning Substitutes that have been SNAP approved for use in Motor Vehicle Air Conditioning (MVAC) applications. Table 6 lists refrigerants that are not approved for use in MVAC applications. SNAP approval does not mean that the alternative refrigerant is compatible with the materials (or lubricant) used in the MVAC system or that the performance of the unit will be similar. SNAP approval only means the environmental effects of the refrigerant are acceptable and the refrigerant has been tested to determine flammability. The EPA has made it illegal to use flammable refrigerants in motor vehicle air conditioning systems except for HFC-152a in new MVAC equipment. Each potential new refrigerant must be tested according to the American Society of Testing Materials (ASTM) E-681 testing method to determine flammability. In addition to testing the refrigerant itself, if a blend contains a flammable component, the EPA requires leak testing, to ensure that if the composition changes during a leak, that it does not become flammable.

The SNAP approval also includes a requirement for unique fittings to be installed on the high and low side service port of the system being retrofitted with the alternative refrigerant as well as unique fittings on the refrigerant cylinders which contain the alternative refrigerant. The unique fittings are part of an effort to minimize cross contamination. Table 7 lists the fittings for the SNAP approved MVAC refrigerants. Only SNAP approved refrigerant substitutes that have been specifically approved for motor vehicle use can be used in MVAC systems.

Some refrigerant blend manufacturers have chosen trademarks that may give the impression the "New" refrigerant is a drop-in for R-12 and have even incorporated the "12" as part of their name (FREEZE-12 for example). However using any substitute refrigerant requires as a minimum that the high-side and low-side service ports be changed to the SNAP designated fittings (Table 7) and the system be re-labeled to indicate the replacement refrigerant contained in the MVAC system. That means there are no refrigerants which can simply be charged into an CFC-12 or HFC-134a system without any hardware changes! There may also be other changes necessary such as new seals, hoses, lubricant, and additional safety devices. The EPA has several publications available on their Internet Site (http://www.epa.gov/ozone/title6/609) or available from their HOTLINE (800-296-1996) which discuss compressor replacements, retrofit procedures, sources for retrofit training, and common Questions and Answers.

Table 5. Refrigerant Blends Containing at Least One Flammable Component 

*R-176 contains CFC-12, HCFC-22. and HCFC-142b. It is a different product from RB-276, typically sold under the name "Freezone."

Even though there are replacement blends on the market that will supposedly replace R-12 with minimal retrofitting, Mainstream is not aware of any automotive manufacturer to this date that has approved a refrigerant blend for an R-12 system. R-134a is recognized as the refrigerant of choice for new mobile air conditioning systems. There has also not been any single refrigerant or blend that is a direct drop-in for R-12 in automotive air conditioning systems. There is always the need for some retrofitting of the system. Finally, most blends and their lubricants are not compatible with the existing R-12 system and will require separate service equipment. Recharging a blend is also quite different, you must always recharge as a liquid.

Retrofitting

Introduction

Never attempt to put any retrofit refrigerant into an existing R-12 automotive system without first retrofitting the system. Retrofit changes may include larger condenser surface areas to control head pressures, a high-pressure cut-out device for safety concerns, different style hoses, newly designed filter-driers, a new compressor, and different internal seals in the compressor and/or other internal parts. Always follow the original equipment manufacturer's recommendations to avoid injury and voiding a warranty. Always use the retrofit refrigerant that has been approved by the original vehicle air conditioning manufacturer.

Although section 609 of the Clean Air Act does not govern retrofitting, Section 612 of the Clean Air Act (which describes the Agency's Significant New Alternatives Policy [SNAP] program), does require that when retrofitting a CFC-12 vehicle for use with another refrigerant, the technician must first extract the CFC-12, must cover the CFC-12 label with a label that indicates the new refrigerant in the system, and must affix new fittings that are unique to the new refrigerant.

In addition, if a technician is retrofitting a vehicle with a refrigerant that contains R-22, the technician must ensure that only barrier hoses are used in the A/C system and if the system includes a pressure relief device, the technician must install a high pressure compressor shutoff switch to prevent the compressor from increasing pressure until the refrigerant is vented.

Much more information about the SNAP program and about retrofitting procedures is available in an EPA fact sheet called "Choosing and Using Alternative Refrigerants" which is available through the EPA Hot Line (800-296-1996) or the EPA Internet site www.epa.gov. The Society of Automotive Engineers (SAE) also has several useful documents including SAE Document J1660, "Fittings and Labels for Retrofit of R-12 Mobile Air Conditioning Systems to R-134a" and SAE Document J1661, "Procedures for Retrofitting R-12 Mobil Air Conditioning Systems to HFC-134a."

Table 7 - Fitting Sizes for Motor Vehicle A/C Refrigerants

Lubricant Change-Over

One of the most important system changes is the lubricant. The lubricant used in a system should always be identified on the unit because of potential lubricant incompatibilities. The mineral oils used with R-12 are not adequately circulated through the A/C system when R-134a is the refrigerant. Automobile manufacturers have tested both PAGs and esters for refrigerant/lubricant miscibility, lubricity, chemical stability and materials compatibility. In the process of developing recommendations, they also considered the additives and conditioners present in the oils. Most of the compressor manufacturers chose to use PAG lubricants in new vehicles equipped with R-134a. Some compressor manufacturers are shipping new compressors with PAGs, some with esters, and some are shipping them empty.

PAG oils are hygroscopic, which means that they will draw water from the atmosphere when exposed. Many aftermarket A/C specialists are choosing to use ester lubricants (POE oils) instead of PAGs, because they believe that the hygroscopic characteristics of PAGs may limit their lubricating ability and introduce corrosion into a the A/C system. POE lubricants are also hygroscopic (although less so than PAGs), and care must still be taken to ensure that excess moisture does not go into the system.

It is good practice to use PVC-coated gloves and safety goggles when handling these lubricants, since prolonged skin contact or even brief eye contact can cause irritations such as stinging and burning sensations. You should also avoid breathing any vapors produced by the lubricants, and make sure to use them in well ventilated areas. Keep both PAGs and POE's in tightly sealed containers, both so that humidity does not contaminate the oil, and so that the vapors do not escape.

The amount of mineral oil that can safely remain in a system after retrofitting, without affecting performance, is still being debated. It was originally thought that 1 to 5% of mineral oil left in the system was acceptable and that any more mineral oil than that could cause compressor failure. Removing the mineral oil may require draining certain components. Unless the vehicle manufacturer recommends flushing the system during the retrofit procedure, a service technician can assume that flushing is not necessary. (Although the SAE J1661 procedure for retrofit includes flushing, according to the EPA's website, SAE no longer believes that flushing is critical to a successful retrofit.)

Hoses and O-Rings

When R-134a was first introduced, it was thought that all non-barrier/nitrile hoses would have to be replaced during an AC retrofit. Early laboratory tests showed that the small R-134a molecules leaked through the walls of non-barrier hoses more readily than the larger R-12 molecules did. In the laboratory, this caused unacceptably high leakage rates. More recent testing, however, has shown that oils used in automotive MVAC systems are absorbed into the hose to create a natural barrier to R-134a permeation. Therefore R-12 system hoses will perform well, provided they are in good condition. Cracked or damaged hoses should always be replaced with new barrier hoses. Most retrofit instructions call for lubricating replaced O-rings with mineral oil to provide this Natural barrier protection.

Desiccants Change-Out during R-134a Retrofit

An MVAC system, like any other vapor compression A/C system, utilizes a filter/drier to remove moisture and acid from the system. These filter/dryers also known as desiccants in the MVAC industry no longer function when they are saturated with moisture or acid. R-12 systems typically use an XH-5 desiccant, while R-134a systems use either an XH-7 or XH-9 desiccant. Some manufacturers recommend routine replacement of the drier to one containing XH-7 or XH-9 during the retrofit procedure. (Any systems with silica gel desiccant MUST be switched to XH-7 or -9 desiccant during the R-134a retrofit.) Manufacturers generally agree desiccant or filter/drier should be replaced if the vehicle has over 70,000 miles or is older than five years, and is opened up for major repair. In that case use the R-134a-compatible desiccants.

Misleading Use of "Drop-in" to Describe Refrigerants

Many companies use the term "drop-in" to mean that a substitute refrigerant will perform identically to CFC-12, that no modifications need to be made to the system, and that the alternative can be used alone or mixed with CFC-12. However, EPA believes the term confuses and obscures several important regulatory and technical points. First, charging one refrigerant into a system before extracting the old refrigerant is a violation of the SNAP use conditions and is, therefore, illegal. Second, the fittings and labels on a system must always be changed if the refrigerant type is changed. Third, certain components may be required by law, such as new hoses and compressor shutoff switches. For all of these reasons, EPA does not use the term "drop-in" to describe any alternative refrigerant.

SNAP Requirement for Unique Service Fittings

As part of the SNAP regulations the EPA requires that each new refrigerant must be used with a unique set of fittings to prevent the accidental mixing of different refrigerants. These unique service fittings are required at the high and low side service ports on the car itself, on all recovery and recycling equipment, and on the refrigerant containers. If the car is being retrofitted, any service fittings not converted to the new refrigerant must be permanently disabled. Unique fittings help protect the consumer by ensuring that only one type of refrigerant is used in each car. They also help protect the purity of the recycled supply of CFC-12, which means it will last longer, so fewer retrofits will be necessary nationwide. The list of fittings is available in an EPA fact sheet titled "Fitting Sizes and Label Colors for Motor Vehicle Refrigerants."

Label Requirements for Retrofits

When a new refrigerant is retrofitted, the technician must apply a detailed label giving specific information about the retrofitted refrigerant. The label's background color is chosen by the refrigerant manufacturer to be unique, and the label colors for each refrigerant are listed in an EPA fact sheet titled "Fitting Sizes and Label Colors for Motor Vehicle Refrigerants." The label for the old refrigerant must be covered or removed. The retrofit label shows:

• the name and address of the technician and the company performing the retrofit;
• the date of the retrofit;
• the trade name, charge amount, and, when applicable, the ASHRAE numerical designation of the refrigerant;
• the type, manufacturer, and amount of lubricant used; and
• if the refrigerant is or contains an ozone-depleting substance, the phrase "ozone depleter"

Barrier Hoses for R-22 Retrofit Blends

R-22 also referred to as HCFC-22 can seep out through traditional hoses. Therefore, when using any refrigerant blend containing R-22, the technician must ensure that new less permeable "barrier" hoses are used. These hoses must be installed if the system currently uses non-barrier hoses.

Compressor Shut-Off Switches

Some MVAC systems have a pressure relief device that automatically releases refrigerant to the atmosphere to prevent extremely high pressures. When retrofitting any system with such a device to use a new refrigerant, the technician must also install a high-pressure shutoff switch. This switch will prevent the compressor from increasing the pressure to the point where the refrigerant is vented.

For More Information on Retrofitting

EPA's Stratospheric Ozone Protection Hot Line (800-296-1996) distributes numerous fact sheets and brochures. The following fact sheets discuss various issues related to motor vehicle air conditioning and ozone depletion.

• Fitting Sizes and Label Colors for Motor Vehicle Refrigerants
• Questions to Ask Before You Purchase an Alternative Refrigerant
• The Facts Behind the Phase Out
• Qs & As on HC-12a, OZ-12, and Other Flammable Refrigerants
• Qs & As on Ozone-Depleting Refrigerants and Their Alternatives

Lubricants

The majority of HFC-134a automotive air conditioning systems use polyalkylene glycols, (PAG), as the lubricant. The conventional R-12 systems used mineral oil lubricants. However, more and more polyol ester (POE) lubricants are being researched and used in mobile applications and are quickly becoming the second generation lubricant with automotive air conditioning systems incorporating R-134a as the refrigerant. PAGs and POEs are very different from the mineral oil lubricants used in conventional R-12 automotive air conditioning systems of the past.

Ever since R-134a/PAG and R-134a/ POE automotive air conditioning systems have entered the market, the service technician has had to pay close attention to which PAG or POE lubricant package is specified for a particular vehicle. Even though most automotive R-134a systems may use a PAG or POE-based stock lubricant, not all lubricant additive packages are the same, and may not be compatible from vehicle to vehicle. Whether the system is new or retrofitted, the service technician must use only the air conditioning manufacturer or vehicle's specified lubricant package. If the system is a newer one, the specified lubricant will be identified on an identification tag located in the engine compartment or on the air conditioning system itself. Never mix lubricants in a system and be careful to avoid unintentional mixing of lubricants in the recovery equipment, cylinders, hoses, and manifold sets. Mixing lubricants can cause serious air conditioning system problems. The proper amount of lubricant is also a very important consideration. If overcharged with lubricant, the system will become oil logged and less efficient, delivering warmer air, or may result in premature compressor failure. Many individuals believe the high incidence of compressor failure in the automotive industry is at least in part caused by lubrication overcharge.

When servicing R-134a systems, it is imperative that care be taken to assure that air and moisture contamination to PAG and POE oils be kept to an absolute minimum. Keep the oil containers closed and hoses sealed-off when not in use. PAG and POE lubricants readily absorb moisture when left exposed to the air. By SAE standards, different hoses are used for R-12 and R-134a systems thereby making it harder to cross contaminate refrigerants. But R-134a systems could be using POE or PAG oils and cross contamination of the oil can result in unwanted chemical reactions in the system and refrigerant breakdown and material corrosion. Always use the lubricant specified by the manufacturer to avoid cross contamination of the oil. If you routinely use more than one type of HFC-134a lubricant, then in order to prevent cross contamination from the oil in the hoses, we suggest using designated separate manifold gauge sets for R-134a with PAG oil and R-134a with POE oils. Remember to always tag the system with the refrigerant and oil being used in the system.

Removing Moisture

As stated above, the new synthetic oils have a much higher attraction for water than did the mineral oils of yesteryear. Moisture in a system, if not removed by the water absorption material in the filter-drier, can freeze at the expansion device and clog the system. Always replace the filter-drier when opening-up a system for repair and never reuse lubricant.

When moisture is excessive a vacuum pump is used to remove moisture from a system before the lubricant and refrigerant is replaced into the system. Moisture can be in either a vapor or liquid state in the system. When the moisture is in the vapor state, it is easy to remove; however, when the moisture is in the liquid state, it is much harder to remove because it must be vaporized, and the vaporization of water in the system further reduces the remaining water temperature, which makes further evaporation more difficult.

For example, if liquid water in the system is initially at 80°F, then the saturation pressure of the water is 28.87 inches of mercury. The vacuum pump must therefore achieve a pressure of at least 28.87 inches of mercury for this liquid water to boil off. As the water cools to 70°F the saturation pressure of the water becomes 29.16" Hg and the vacuum pump must achieve a pressure of 29.16" Hg for the remaining water to boil off. Once again, however, the further evaporation of water will further cool the remaining water. If the water is cooled to 50°F, then the vacuum pump must achieve a pressure of 29.54 for the remaining water to boil off. As you can see, it becomes very difficult to remove liquid water from the system, and if the water evaporates too fast, it will cool below the freezing point of water and freeze, essentially halting vaporization.

If moisture must be removed, the following guidelines may be helpful.

1. Use a vacuum pump with clean vacuum pump oil. (Dirty vacuum pump oil will limit the vacuum achievable by the vacuum pump.)
2. Do not add the air conditioner's compressor oil back into the system until after the evacuation. If you add it earlier, the oil may become wet and hard to evacuate. The new POE oils have a very high affinity for water.
3. Use a heat lamp to apply heat to the system. The entire system, including the interconnecting piping, must be heated to a warm temperature or the water will boil to a vapor where the heat is applied and condense where the system is cool. If this happens the water is just being moved around, but not being removed.
4. Start the vacuum pump and observe the oil level in it. As moisture is removed, some of it will condense in the vacuum pump's crankcase. Some vacuum pumps have a feature called gas ballast, that introduces some atmosphere between the first and second stages of the two-stage pump. (This is typically not necessary in automotive applications.) This prevents some of the moisture from condensing in the vacuum pump's crankcase. Regardless of the vacuum pump, watch the oil level. Over a period of time, water in the vacuum pump will displace the oil and raise the oil out of the pump. Eventually, water may be the only lubricant in the vacuum pump crankcase, and damage may occur to the vacuum pump. Since automotive systems typically do not have tremendous quantities of water in the system, if you change the vacuum pump oil on a periodic basis, you will avoid this problem. (Check the vacuum pump oil for water when you replace the oil.)
5. Isolate the system, and crack the line to the vacuum pump, before turning the vacuum pump off. This allows air to enter the line thereby keeping vacuum pump oil from being drawn into the hose.

Non-Condensable Gas Determination and Removal

If the refrigerant temperature is known and the measured pressure is above the saturation pressure, (for that temperature), then the refrigerant is contaminated with either non-condensable gases or another refrigerant. SAE has developed a Recycled Refrigerant Checking Procedure to determine if Non-Condensable gases are present in refrigerant contained in a portable recovery cylinder. This procedure is not to be used on refrigerant that is still located in the A/C unit. The procedure is discussed in detail in SAE Standard J1990 and key features are repeated below.

1. To determine if the recycled refrigerant, in a recovery container, has excess non-condensable gases (air), the container must be stored at a relatively constant temperature of 65°F, or above for at least 12 hours and protected from exposure to direct sun.
2. Install a calibrated pressure gage, with 1 psig divisions, to the container and determine the container pressure.
3. With a calibrated thermometer, measure the air temperature within 4 inches of the container surface.
4. Compare the observed container pressure and air temperature to values on the Non-Condensable Determination Table, to determine if the container exceeds the pressure limits found on the appropriate table. If the refrigerant is R-12 use Table 8, if the refrigerant is R-134a use Table 9. (For Example: for a measured air temperature 70°F, the pressure of a R-12 recovery tank must not exceed 80 psig.)
5. If the container pressure is less than the appropriate table value the non-condensable gas limit has not been exceeded for the refrigerant.
6. If the measured pressure is greater than the appropriate table value, very slowly recover, from the top of the container, a small amount of vapor into the recycle equipment, until the pressure is less than the pressure shown on the appropriate table. (Venting must be performed very slowly, otherwise, the container will cool itself and alter the refrigerant temperature.) If this self-cooling does occur, the container must be given time to reach a stable temperature again, that is repeat the procedure from Step 1.)
7. If the container still exceeds the pressure shown on the appropriate table, the entire contents of the container must be recycled. 

Table 8. R-12 Non-Condensable Determination Table 

Table 9. R-134a Non-Condensable Determination Table

Automotive Hose Assemblies

Basic Design of Automotive Hose Assemblies

Automotive air conditioning systems utilize a combination of metal tubing and rubber hoses. The rubber hoses are connected to the metal tubing with a barbed tubular section that is inserted into the rubber hose. The barbs are necessary to keep the metal tube from sliding out of the hose, when the system is pressurized. The rubber hose with the barbed tube inserted inside is then clamped with a metal Ferrule. The Ferrule is crimped to a smaller diameter thus clamping the rubber hose to the metal tube. The refrigeration hose is a special barrier type hose that is compatible with refrigerants in the system, capable of sustaining the worst case system pressures, and has low refrigerant permeability.

Leak Checking

When leak checking any part of the system, always look for oil deposits, since an oil residue typically indicates a source of leaks. This is because both oil and refrigerant leak out, but the refrigerant vaporizes leaving an oil residue. If a leak is discovered in the rubber hose or at the point where the rubber hoses attaches to the metal tube, the hose assembly should be repaired or replaced. In many cases the metal tubing portion of the plumbing assembly is not damaged,  rather it is the flexible hose that is leaking. In this case the rubber hose can be replaced, provided the same type of hose can be obtained.   Many aftermarket suppliers offer replacement barrier refrigerant hoses along with the necessary hose clamping tools and instructions. Always verify that the replacement hose is compatible with the actual refrigerant being used in the A/C system. HCFC-22, a component in some blends, and can seep out through many common traditional hoses. Therefore, when using a blend,  you must verify that the new, less permeable barrier hoses developed specifically for HCFC-22 are used. These hoses must also be installed if the system currently uses old, non-barrier hoses and the refrigerant is being changed.

Hose Repairs

To replace the rubber hose on a A/C plumbing assembly, requires a hose repair kit.  Never attempt to crimp the metal Ferrule with a vice or pliers, and never use a radiator hose clamp on the refrigeration hoses. Never use air hoses  for refrigerant. Always, follow the hose repair crimping tool instructions supplied with the actual kit. The hose repair procedure can be generally described in a four step process.

Step 1. Cut the original Ferrule, so that the ferrule can be spread open and removed from the Hose.

Step 2. Remove the barbed tube from inside the rubber hose. This may require cutting the rubber hose to free the barbed tube. If the hose is cut, be carful not to scribe a line in the tube while cutting the hose free. If the barbed tube does get scratched, it will be a source of leaks and the tube will have to be replaced.    The barb must be cleaned of any old hose debris before reusing. Inspect the barb to be sure there are no rough edges, replace the metal tube assembly, if necessary.

Step 3. Install a new replacement Ferrule onto the metal hose as well as a new retaining ring. Then slide the barbed section of the tube into the new rubber hose. Never reuse an old hose. Be sure that the hose is slide all the way onto the Barb.

Step 4. Using the Crimping tool (supplied for the Ferrule and hose diameter being used), crimp the ferrule onto the hose.

Step 5. After replacing the tubing assembly, leak check the system with nitrogen, before recharging the system with refrigerant.

Key Recommended Recovery/Recycle Service Procedures

1. Verify the vehicle air conditioner has refrigerant pressure. (If no pressure is present in the system, do not use the recovery unit.)
2. Reduce system pressure until a vacuum is reached and held.
3. Heat, (from a heat lamp), may be applied if the system shows evidence of icing. Never heat with an open flame.
4. Determine the amount of lubricant removed during the refrigerant removal process and add new lubricant. (Discard used lubricant, Never Reuse Lubricant)

Recommended Service Procedures for Using a Manifold Gauge Set

1. High-, Low- and Center-Service hoses must have shut-off valves within 12 inches (30 cm) of their service ends. These valves must be closed prior to hose removal from the air conditioning system. This will reduce the volume of refrigerant that would otherwise be vented to the atmosphere.
2. During all service operations, the valves should be closed until connected to the vehicle air conditioning system or the charging source to avoid introduction of air and to contain the refrigerant, rather than vent to the atmosphere.
3. When the manifold gauge set is disconnected from the air conditioning system or when the center hose is moved to another device that cannot accept refrigerant pressure, the gauge set hoses should first be attached to the recovery/recycling equipment, to recover the refrigerant from the hoses.
4. Never trap liquid refrigerant in a hose. As the refrigerant heats up during the day, the increase in pressure can cause the hose to burst.

Recovery-Only Equipment Requirements

R-12 Recovery-Only Equipment

Refrigerant recovery equipment must be certified by to meet the appropriate recovery standard. Equipment that recovers but does not recycle CFC-12 refrigerant must meet SAE standard J2209. The key functions are described below.

1. The recovery equipment must be capable of removing a minimum pressure of 102 mm of Mercury below atmospheric pressure.
2. The equipment  must be capable of continuous operation in ambient temperatures between 50°F and 120°F.
3. The equipment must be able to separate lubricant from recovered refrigerant and accurately indicate the amount removed from the system.
4. Since January 1, 1992, all recovery hoses must meet SAE J2196 specifications and must have a shut-off device within 12 inches (30 cm), of the connection point to the MVAC.
5. The equipment must have an 80% full shut-off device and a mechanical pressure relief valve.
6. The equipment must meet be certified to meet  the SAE J2209 standard.
7. The EPA will maintain a list of approved equipment by manufacturer and model.

R-134a Recovery-Only Equipment

Since October 31, 2008, equipment that recovers but does not recycle HFC-134a refrigerant must be certified to meet EPA requirements as set forth in SAE standard J2810—HFC-134a (R-134a) Recovery Equipment Mobile Air-Conditioning Systems. The key functions are described below.

1. The recovery equipment must be capable of removing a minimum of 95% of the refrigerant from the test system in 30 minutes or less.
2. The equipment  must be capable of continuous operation in ambient temperatures between 50°F and 120°F.
3. The equipment must be able to separate lubricant from recovered refrigerant and accurately indicate the amount removed from the system.
4. Since January 1, 1992, all recovery hoses must meet SAE J2196 specifications and must have a shut-off device within 12 inches, (30 cm), of the connection point to the MVAC.
5. The equipment must have an 80% full shut-off device and a mechanical pressure relief valve.
6. The equipment must meet be certified to meet  the SAE J2810 standard.
7. The EPA will maintain a list of approved equipment by manufacturer and model.

The purpose of  SAE standards for the recovery equipment is to provide minimum performance and operating feature requirements for the recovery machines used to recover refrigerant that is to be returned to a refrigerant reclamation facility (that will process it to the appropriate ARI 700 Standard or allow for recycling of the recovered refrigerant to SAE specifications by using certified recovery equipment).

Refrigerant  removed from a MVAC system with recovery equipment can not be returned to a mobile A/C system because recycling (with a certified unit) is required before used refrigerant can be returned to a system.

Recovery/Recycling Equipment Requirements

R-12 Recovery/Recycling Equipment

Refrigerant recovery/recycling equipment must be certified by the EPA Administrator or an independent organization approved by the Administrator to meet the appropriate recovery standard. Equipment that recovers and recycles CFC-12 refrigerant must meet SAE standard J1990. The key functions are described below.

1. The recovery equipment must be capable of removing a minimum pressure of 102 mm of Mercury below atmospheric pressure.
2. The equipment  must be capable of continuous operation in ambient temperatures between 50°F and 120°F.
3. The equipment must be able to separate lubricant from recovered refrigerant and accurately indicate the amount removed from the system, in 30mL units.
4. Since January 1, 1992, all recovery hoses must meet SAE J2196 specifications and must have a shut-off device within 12 inches, (30 cm), of the connection point to the MVAC.
5. The equipment must have an 80% full shut-off device and a mechanical pressure relief valve.
6. The equipment must meet be certified to meet the SAE J1990 standard.
7. The equipment must purify refrigerant to SAE J1991 Standard.
8. The EPA will maintain a list of approved equipment by manufacturer and model

R-134a Recovery/Recycling or Recovery/Recycling/Recharging Equipment

Since January 1, 2008, equipment that recovers and recycles HFC-134a refrigerant and equipment that recovers and recycles HFC-134a refrigerant and recharges systems with HFC-134a refrigerant must be certified to meet EPA requirements as set forth in SAE standard J2788—HFC-134a (R-134a) Recovery/Recycling Equipment and Recovery/Recycling/Recharging for Mobile Air-Conditioning Systems.

In the past, recovery/recycling  equipment for MVAC applications was designed to meet SAE standard J2210. However, an industry sponsored research project, has shown that equipment that was designed to meet this SAE standard (J2210) would not recover all the refrigerant from MVAC systems. This study indicated that as much as 30% of refrigerant remained in an MVAC system,  while the SAE J2210 certified recovery equipment indicated all refrigerant had been recovered. While the “proper” procedure to follow after opening a system for repair is to perform a triple evacuation of the system to remove residual moisture or refrigerant, many MVAC service technicians skip this step, electing instead to rely on the recovery machine to completely evacuate the system.

In appears that in cases where only the refrigerant charge was being removed and replaced, the MVAC recovery recycling machine was being used to recover the system, evacuate the system and recharge the system. In these cases, if the MVAC service technicians relied on the refrigerant recovery recycling machine to assure complete recovery, a failure to properly recovery all the refrigerant could lead to a system overcharging by as much as 30%.

To remedy this potential problem, the SAE has revised its requirements for recovery recycling machines. The SAE replaced standard J2210 with standard J2788 in October 2006. SAE standard J2788 encompasses all of the features of J2210, while adding additional standards on recharging of MVAC systems, and adding performance standards to improve equipment refrigerant recovery performance. SAE Standard J2788 includes a recharge accuracy requirement of 0.5 ounce and requires approved designs to be tested to very they recovery 95% of the refrigerant from an MVAC system.

The EPA has updated the recovery recycling requirements reference from J2210 to J2788, for recovery/recycling equipment and for recovery/recycling/recharging equipment. In addition, for purposes of clarity, EPA has added a clause to Section 82.34 (Prohibitions and required practices), which specifies that equipment manufactured or imported must meet the SAE standards.

Currently the EPA regulations under Sec. 82.36 (Approved refrigerant recycling equipment) encompass more than just refrigerant recycling and includes refrigerant recovery. Therefore, to more accurately reflect the provisions outlined in that section, EPA is revising the title of Sec. 82.36 from “Approved refrigerant recycling equipment'' to “Approved refrigerant handling equipment.''

While the EPA has updated the refrigerant handling equipment requirements, it did not require an immediate replacement of previously certified MVAC recovery and recovery/recycling equipment with new J2788 certified equipment. Rather, all new MVAC Recovery/Recycling and Recovery/Recycling/Recharging equipment for MVAC systems manufactured after December 31, 2007 must be certified to J2788. MVAC shop owners are not required to replace their old J2210 certified equipment, however they may decide to replace old J2210 equipment with the new J2788 equipment because of the additional refrigerant savings that translate into a cost savings. According to the January 2007 Mobile Air Conditioning Society Worldwide (MACS) Service Report, the new J2788 equipment will result in a 30% to 50% refrigerant savings because the equipment will recover more refrigerant from an MVAC system. The recovered refrigerant can be recycled for future use, rather than buying new refrigerant.

The complete functional description of  Recovery/Recycling and Recovery/Recycling/Recharging  equipment for MVAC applications is more fully explained in SAE Standard J2788 (section 7, page 4), however the key functions are described below.

1. The recovery equipment must be capable of removing a minimum of 95% of the refrigerant from the test system in 30 minutes or less.
2. The equipment  must be capable of continuous operation in ambient temperatures between 50°F and 120°F.
3. The equipment must be able to separate lubricant from recovered refrigerant and accurately indicate the amount removed from the system.
4. The refrigerant recovered, after oil separation, must be measured and the quantity displayed. The quantity displayed, which represents the actual refrigerant removed, must be accurate  to within plus or minus one ounce (30 grams).
5. Since January 1, 1992, all recovery hoses must meet SAE J2196 specifications and must have a shut-off device within 12 inches, (30 cm), of the connection point to the MVAC.
6. The equipment must have an 80% full shut-off device and a mechanical pressure relief valve.
7. The equipment must meet be certified to meet  the SAE J2788 standard.
8. The equipment must purify refrigerant to SAE  Standards.
9. The EPA will maintain a list of approved equipment by manufacturer and model.

Topping Off Regulations

The January 29, 1998 Final Rule clarifies an existing provision of the Section 609 EPA Clean Air Act regulations. The rule explains that Quick-Lubes and other facilities that charge refrigerant into vehicles but do not perform any other kind of refrigerant servicing or repair (i.e., facilities that "top off" only) are still considered to be performing service involving refrigerant, and are therefore subject to all the requirements of the Section 609 regulations, including the requirement that they must purchase approved equipment and the service performed by MVAC certified technicians.

In addition, the EPA does not require recovery and recycling of the refrigerant contained in a system prior to topping off the system with additional refrigerant.

Dual-Refrigerant Recovery Equipment

Refrigerant recovery equipment which can recover two different refrigerants is available. The concern with the use of such dual refrigerant recovery devices is the potential for cross-contamination of the refrigerant which is being recovered. The EPA has adopted SAE Standard J1770 which incorporates many safeguards to prevent cross contamination. For example any single-circuit dual-refrigerant equipment must contain special features to prevent cross contamination in the refrigerant circuit. The equipment must prevent the initiation of the recovery operation if the equipment is not set up properly. If an operator action is required to clear the unit prior to reconnecting for a different refrigerant, the equipment shall be provided with a means which indicates which refrigerant was last used. The equipment is also required to prevent recovery from two different refrigerant sources concurrently. The standard also specifies that the transfer of recycled refrigerant for recharging and transfer must be from the liquid phase only, this is to allow proper recharging of refrigerant blends which must be charged from the liquid phase.

Recycling Blends

Once recovered, only uncontaminated CFC-12 or HFC-134a should be recycled on-site. Recovering contaminated R-12 or R-134a refrigerant into recycling equipment may damage the equipment, and recovery equipment can only filter and dry refrigerant it can not remove other gaseous impurities such as air or other refrigerants. Furthermore, EPA regulations prohibit technicians from recycling blend substitute refrigerants whether they are contaminated or not. This is because a blended refrigerant could have lost one or more of the volatile components of the blend (due to system leaks), and this can dramatically change the performance characteristics of the blend. Recycling can not replace the lost constituents of the blend.

Refrigerants in Use

Recovery, recycling and recharging of automotive A/C systems is a lot more complicated than it used to be. In the past, all automotive A/C systems used CFC-12, however, this is clearly not the case anymore. Even when R-12 was the only refrigerant in town, many A/C techs discovered systems that had been contaminated with air, HCFC-22 or even hydrocarbons like propane and butane.  

In addition to the new vehicles that are using HFC-134a refrigerant, there is an astonishing number of  R-12 substitutes in the market. Clearly,  the variety of refrigerants that technicians can encounter is making A/C service more complicated.

The EPA requires that when any vehicle is retrofitted from R-12, a label identifying the new refrigerant in the system must be placed under the hood, and new unique fittings must be attached to the high- and low-side service ports of the A/C system (see Table 7). Of course you could encounter a vehicle that has been retrofitted to another refrigerant but has not been properly relabeled, or a vehicle that has the right label, but highly contaminated refrigerant. Propane is not a legal automotive refrigerant, so if this refrigerant is used, chances are little warning will be provided.

Checking refrigerant pressures does not guarantee that you will recognize that refrigerant is contaminated or is a brand that is unfamiliar to you. Unusual head pressures can indicate an improperly labeled system, however, a contaminated system can result in a similar pressure temperature dependence.

Purchasing a refrigerant identifier unit can help pinpoint many refrigerant identification problems, and EPA strongly recommends, but does not require, this equipment. Some identifiers are simple go/no-go devices that only tell you if the refrigerant is HFC-134a or not (or CFFC-12 or not). Alternatively there are more sophisticated and expensive diagnostic units that indentify the constituents and even identify flammable working fluids. SAE Standard J1771 applies to refrigerant identification equipment to be used for identifying refrigerant CFC-12 (R-12) and HFC-134a (R-134a) refrigerant when servicing MVAC systems.

In general however, even the most sophisticated portable diagnostic units on the market today cannot properly identify all combinations of chemicals used in blend refrigerants. Diagnostic identifiers being sold today typically can identify potential R-12 and R-134a contaminants such as air, R-22, and flammable hydrocarbons, but many were not designed to identify R-124 and R-142b (chemicals that are components in many of the new substitutes), or to recognize particular chemical combinations as a specific commercial blend.

Whether you are interested in purchasing a "go/no-go" unit or a diagnostic unit, check that the unit meets the SAE J1771 standard, which is an indication that the unit accurately identifies refrigerants. When claiming to meet this standard, manufacturers of identifier equipment are required to state the accuracy of the unit.

Charging of MVAC Systems

The most accurate method of charging a MVAC system (after repairing and leak checking the system) is to:

1. Leak Check the system with dry nitrogen at a pressure of 100 to 150 psig.
2. Properly evacuate the system to at least 29 inches of mercury,
3. Add the lubricant to the system
4. Re-evacuate the system to at least 29 inches of mercury
5. Charge the system using a refrigerant charging scale or other accurate refrigerant metering device (accuracy should be at least 0.5 ounce of charge)

When charging directly from a refrigerant cylinder, connect a manifold gauge to both the high and low side service ports of the MVAC, and initially introduce the refrigerant into the both the high- and low-side of the system. Once the pressure of the system is above the saturation pressure at 40°F, start the compressor and continue to add charge to the low-side of the system until the proper quantity of refrigerant has been added to the system (as determined from the charging scale or charging meter). 

When charging the MVAC system with a pure refrigerant such as R-134a, R-12, or R-152a then you should charge as a vapor to avoid refrigerant slugging and to slow the charging process (and avoid over charging). 

When charging the MVAC system with a blended refrigerant, instead of a pure refrigerant, then you must remove the refrigerant from the storage tank as a liquid.  This may involve inverting the storage container or using a different connection to the tank.  The refrigerant must be removed from the storage tanks as a liquid.  The manifold valve should be almost completely closed, so the liquid from the refrigerant tank flashes across the valve on the charging manifold and the refrigerant actually enters the MVAC system as a vapor. The refrigerant should be slowly introduced into the compressor, if any unusual noise (slugging) is heard, immediately shut off the flow of refrigerant (at the manifold valve) and resume charging at an even slower rate (with the manifold valve closed even more).

If a HFC-134a recovery/recycling/recharging machine is being used, and it has been manufactured after January 1, 2008, and is properly operating, it has been certified to meet EPA requirements as set forth in SAE standard J2788 (HFC-134a Recovery/Recycling Equipment and Recovery/Recycling/Recharging for Mobile Air-Conditioning Systems). This system will recover at least 95% of the refrigerant in a MVAC system and provide a re-charging accuracy of  at least 0.5 ounce.  Follow the manufacturer's instructions for using their unit.  If you are using an older machine (that is not certified to meet SAE standard J2788), they have been shown to leave as much as 30% of the refrigerant charge in the system  and this can result in system over charging, compressor slugging and added refrigerant expense. For these older machines, it is suggested that you manually override the automatic recovery operation to assure complete refrigerant recovery and proper system recharge.

Incorrect Calculation of Charge

Vapor compression air conditioning systems, like those used in MVAC systems, have several options for the configuration of the throttling expansion valve.  The expansion valve can be a feedback type control valve that adjusts the opening to accurately control evaporator exit superheat, such as a Thermostatic Expansion Valve (TXV) or it can be a fixed orifice, such as an orifice plate or capillary tube.  The advantage to the  TXV type valve is that it closely controls evaporator exit superheat, even if the operating charge is not perfect.  Fixed orifices on the other hand, have the evaporator superheat closely related to the system charge. 

If too much refrigerant charge is added to a fixed orifice MVAC system the desired superheat will be lost and liquid refrigerant could be returning to the compressor, resulting in compressor slugging and premature compressor failure. 

If too little refrigerant charge is added to a fixed orifice MVAC system, the  superheat will be excessive, resulting in reduced cooling capacity and if the charge is far too low, it will lead to icing of the evaporator coil (typically on cooler or rainy days). 

Most of today's MVAC systems use a fixed orifice type expansion (to save cost)  and therefore maximum cooling capacity and proper system life is highly dependent on having the proper charge. 

If the system is properly evacuated and charged with a SAE standard J2788 certified Recovery/Recycle/Recharge machine, an accurate charge should be introduced. 

If the MVAC system is being topped off, then the total quantity of charge in the system can not be determined.  For this reason alone, Mainstream does not recommend topping off the refrigerant charge in a system.  It is important to note that the time necessary to top off the refrigerant, wait for the system to equalize, measure the evaporator superheat and condenser subcooling (to determine if the charge is correct) and then repeat the process until the proper charge is obtained will take much more time than simply recovering, recycling and recharging the system - there is no economic incentive to top off  the system if you plan on doing it right!  Of course, if the refrigerant is a blend, it can never be topped off, since the composition of the blend is altered when some refrigerant leaks out of a system, and so the refrigerant must be replaced.  Blended refrigerants can not be recycled, they must be recovered and returned to a refrigerant recycling site. 

If a system is being recharged without an automated recharging machine, then a charging scale, charging cylinder or other accurate refrigerant measuring device (accurate to 0.5 ounce of charge) is necessary. Always completely evacuate the system to a vacuum of at least 29 inches of mercury before any manual charging operation.

Calibration of Recovery and Recharging Machines

Equipment Requirements

R-134a recovery/recycling/recharging systems must be certified to meet SAE Standard J2788 and this standard requires that the equipment must be capable of indicating and recharging the system to within 15 grams (0.5 oz.) of the vehicle manufacturer's specifications.  The standard also requires that if a scale is used by the recharging equipment to determine the quantity of refrigerant recharged then the equipment manufacturer must provide a method or service procedure for the technician to use  to check the accuracy and calibrate the machine. Similarly, if a mass flow system is used for charge determination, the equipment manufacturer must provide a method for checking the accuracy and include any necessary accuracy testing devices with the machine. 

In general to verify or calibrate a refrigerant recovery or recharging scale; the procedures in the next subsections can be used.

Procedure to Verify the Accuracy of a Recharging Unit

1. Place a empty approved refrigerant recovery tank on a platform scale.  The platform scale must have the capacity for measuring the weight of an external recovery tank plus an additional 1000 grams (35 ounces).  The scale must have a accuracy of at least +/- 3 grams  (+/- 0.006 lb).
2. Connect the hoses to the recovery tank from the recharging machine, as if the recovery tank were a MVAC unit.
3. Open the access valve on the recovery tank
4. Record the Initial Weight of the recovery tank
5. Set the Recharging unit to recharge  457 grams (16 ounces) of refrigerant.
6. When recharging is complete, record the Final Weight of the recovery tank
7. Subtract the Final Weight of the Recovery tank (step 6) from the Initial Weight (step 4), the difference is the quantity of refrigerant recharged by the Recharging machine.
8. The quantity of refrigerant recharged should be between 442 grams (15.5 ounces) and 472 grams (16.5 ounces).  If the actual recharged amount as determined in the previous step is more than 472 grams or less than 442 grams the machine must be recalibrated, following the manufacturer's recommendations or returned to the manufacturer or other calibration company for recalibration.

Procedure to Calibrate a Recovery or Recharging Unit

As stated above, SAE J2788 certified Recovery/Recycle/recharge machines are required to provide calibration tools and instructions, and these instructions will supersede anything presented here.  If no other calibration information is available, the general procedures provided in this section should be employed.

A) Inspect the scale and/or the manufacturer's literature to determine if the recharging system has a recharging calibration adjustment mechanism.  

B) If a Calibration Adjustment Mechanism is available on the Equipment, then;

1. Continuing  from the Accuracy Check Procedure above, the actual quantity of  refrigerant recharged was determined in Step 7.  If the actual recharged amount is greater than 457 grams (16 ounces),  then adjust the calibration scale to decrease the quantity of refrigerant recharged.  Similarly, if the actual recharged amount is less than 457 grams,  then adjust the calibration scale to increase the quantity of refrigerant recharged. Turn the adjusting mechanism as little as possible during the initial adjustment, to get a feel for the sensitivity of  this adjustment.
2. Repeat the Accuracy Test.  If the actual recharged amount (from the repeated test) is now within the allowable range of 442 grams (15.5 ounces) to 472 grams (16.5 ounces) then calibration is complete.  If it is outside this range repeat these calibration Steps B-1 and B-2.

C) If a Calibration Adjustment Mechanism is NOT available on the Equipment and the Equipment uses a Platform Scale, then;

1. Continuing from the Accuracy Check Procedure above, the actual quantity of refrigerant recharged was determined in Step 7.  If the actual recharged amount is greater than 457 grams,  then subtract 457 from the actual amount, to determine the amount of weight (in grams) to add to the platform scale (or the tank on the scale)  being calibrated.   For example if the actual recharged amount was 477 grams, the amount of weight to add to the scale would be 477-457, or 20 grams.  Alternatively, if the actual recharged amount is less than 457,  then subtract the actual recharged amount from 457 to determine the amount of weight (in grams)  to remove from the platform scale (or the tank on the scale) being calibrated.  It may not be possible to remove weight, if this is the case simply set the equipment to recharge the additional weight calculated above.  For example, if you set the equipment to recharge 457 grams but the actual recharged amount is 427 grams, the amount you need to take off the scale is 457-427, or 30 grams.  If you cannot remove 30 grams from the scale or tank, simply set the equipment to recharge 487 grams, or 457+30.
2. Add or remove the required weigh to/from the Platform scale or the Recovery Tank
3. Repeat the Accuracy Test.  If the actual recharged amount (from the repeated test) is now within the allowable range of 442 grams (15.5 ounces) to 472 grams (16.5 ounces) then calibration is complete.  If it is outside this range repeat calibration steps C-1 through C-3.

Prevention of Cross-Contamination

Measures must be taken by the service technician to assure cross contamination does not occur while servicing an automotive air conditioning system or recovering refrigerant. Cross contamination can result in chemical reaction of substances within the system, lubrication problems leading to component damage, and decreased performance. During system charging, the specified weighed in amount and approved type of refrigerant for the system must be installed without substitution. Likewise, when replenishing oil, the specified oil for a given refrigerant, and specified by the manufacturer, must be charged into the system.

In service practice, if a recovery machine is attached to a cross contaminated system and that crossed refrigerant charge is recovered, the recovery machine must be cleaned and filter-driers replaced. If the recovered refrigerant is not marked as cross contaminated and properly disposed of, it could be accidentally used again thereby contaminating other air conditioning units. The contaminated, recovered refrigerant must be labeled as Cross Contaminated Refrigerant and picked up for incineration at an approved destruction site, (at significantly increased cost). On-site detection of cross contamination of an AC system before adding the recovered refrigerant to your stored refrigerant is an excellent precaution to prevent contaminating the entire batch of recovered refrigerant. Accurate refrigerant and oil identification prior to any system service procedure is a very important first step in prevention of cross contamination. Different service hose fittings have been specified by SAE to prevent the mixing of R-12 and R-134a, however vehicles coming into today's shops could have any number of strange blends, including flammable gasses, as discussed in the prior Refrigerants in Use section.

Refrigerant and oil, left in the gauge manifold and service hoses, can be a major source of system contamination. When servicing R-134a systems, it is imperative that care be taken to assure that air and moisture contamination to PAG and POE oils be kept to an absolute minimum. Keep the oil containers closed and hoses sealed-off when not in use. PAG and POE lubricants readily absorb moisture when left exposed to the air. By SAE standards, different hoses are used for R-12 and R-134a systems thereby making it harder to cross contaminate refrigerants. But R-134a systems could be using POE or PAG oils and cross contamination of the oil can result in unwanted chemical reactions in the system and refrigerant breakdown and material corrosion. Always use the lubricant specified by the manufacturer to avoid cross contamination of the oil. In order to prevent cross contamination from the hoses, we suggest using designated separate manifold gauge sets for R-134a with PAG oil and R-134a with POE oils.

Used Refrigerant

Recharging Used Refrigerant

The EPA's definition of MVAC "service involving refrigerant," states that MVAC technicians must recycle refrigerant prior to recharging it into an MVAC or MVAC-like appliance, even if the refrigerant is to be replaced back into the same AC unit it was removed from. This is quite different from the HVAC Section 608 requirement for stationary (Non-MVAC) air conditioning and refrigeration applications which allows technicians to transfer refrigerant back into the unit it was removed from or into any other unit owned by the same person without recycling or processing the refrigerant in any way. This requirement is not new and has in fact been clarified in the January 1998 Final Rule summary. This requirement does not apply if the service is not for consideration, as in the case of do-it-yourselfers.

Purchasing Used Refrigerant

EPA regulations prohibit the sale of any used refrigerant, with the exceptions of refrigerant used and intended for use in MVAC or MVAC-like appliances, unless it has been reclaimed by an EPA-certified reclaimer (Sec. 82.154(g)). In the December 30, 1997, amendments to the MVAC recycling regulation explicitly permitted refrigerant recovered from MVACs and MVAC-like appliances at disposal facilities to be reused (after recycling in 609-certified recycling equipment) in MVACs and MVAC-like appliances without being reclaimed.

These requirements, also apply to any working fluid which is a SNAP approved substitute refrigerant for any  MVAC or MVAC-like appliances.

R-12,R-134a, and other air conditioning refrigerants are used in other non-MVAC appliances in addition to being used in MVAC systems.  Refrigerant from non-MVAC equipment should never be recycled and recharged into MVAC systems because non-MVAC systems have many different contaminants not normally present in MVAC systems. For the same reason, MVAC recycle/recharge equipment should never be used with refrigerants obtained from non MVAC equipment. However reclaimed refrigerant from any source can be used in MVAC systems since reclaimed refrigerant must be tested to verify it meets the ARI 700 purity standard for new refrigerant.

Specifically;

• Only section 609-certified technicians or disposal facility owners or operators may recover the refrigerant.
• The refrigerant recovered from the MVACs and MVAC-like appliances may not be mixed with refrigerant from any other sources.
• Only section 609-certified recovery equipment may be used to recover the refrigerant.
• The refrigerant can only be reused in MVAC or MVAC-like appliances.
• The refrigerant can only be sold to 609-certified technicians.
• The section 609-certified technicians must recycle the refrigerant in section 609-certified recycling equipment before charging it into the MVAC or MVAC-like appliance.

These restrictions are intended to ensure that the exemption from the reclamation requirement for refrigerant removed from and charged into MVACs and MVAC-like appliances does not compromise the purity of refrigerant flowing into the MVAC and MVAC-like appliance service sectors.

Disposal facilities must retain signed statements attesting to the removal of the refrigerant from the MVAC or MVAC-like appliance.

Refrigerant Transfer

Any portable container used for transfer of reclaimed or recycled refrigerant must meet DOT and UL standards. Prior to the initial introduction of refrigerant into an approved storage cylinder, (or the changing of refrigerant), the cylinder must be evacuated to at least 27 inches of mercury vacuum. Also, cylinder safe filling level must be controlled by measured weight and liquid net weight must not exceed 80 percent of the cylinder's internal volume.

R-134a

HFC-134a, (R-134a), is the refrigerant that is replacing R-12 in automotive air conditioning systems. The automobile industry has accepted R-134a because of its low hose permeability, along with satisfactory efficiencies. R-134a is a very polar molecule, which contributes to its low solubility in non-polar lubricants such as mineral oils and therefore new lubricants had to be developed.

R-134a is not corrosive on standard steel, aluminum and copper samples. R-134a is regarded as one of the safest refrigerants yet introduced, based on current toxicity data. The chemical industry's Program for Alternative Fluorocarbon Toxicity Testing (PAFT) tested R-134a in a full battery of laboratory animal toxicity studies. The results indicate that R-134a does not pose cancer or birth defects hazard.

OEM engineers and chemical manufacturers have examined the flammability and corrosiveness of each potential R-12 substitute. Like CFC-12, R-134a is not flammable at ambient temperatures and atmospheric pressures. However (as with all refrigerants) service equipment and vehicle A/C systems should never be pressure tested or leak tested with compressed air. Such poor service practices introduce moisture and incompatible (air compressor) mineral oils into the system, but even more important is that some mixtures of air and R-134a have been shown to be combustible at elevated pressures. These mixtures may be potentially dangerous, causing injury or property damage. Some mixtures of air and R-22 are also combustible.

When handling R-134a, as with any other refrigerant, you should be sure to work in a well ventilated area. In the case of a large spill, leave the area immediately. Refrigerants are heavier than air and will displace the air in a room leaving no oxygen available to breathe.

Service Equipment and Specifications

One of the major drawbacks of PAG lubricants is their incompatibility with chlorine and other lubricants. Because of this, service facilities must dedicate separate recovery and recycling equipment along with service hoses and manifold sets for individual refrigerants such as R-12 and R-134a. If this is not done, any residual chlorine and/or mineral oil from the R-12/mineral oil system can contaminate the R-134a/PAG system.

Because R-134a has a smaller molecular size than R-12, it tends to leak out of service hoses more quickly than R-12. For this reason, SAE has mandated different service hose specifications for R-12 and R-134a.

R-12 Service Hoses

The hose, for connecting to the high side of an R-12 MVAC system, will be solid red or black with a red stripe. The hose, for connecting to the low-side of a MVAC R-12 system, will be solid blue or black with a blue stripe. Utility hoses, for R-12, will be either solid yellow or white, or black with a yellow or white stripe. All hoses designed for R-12 use will be marked SAE J2196.

R-134a Service Hoses

The hose, for connecting to the high-side of an R-134a MVAC system, will be solid red with a black stripe. The hose, for connecting to the low-side of a R-134a MVAC system, will be solid blue with a black stripe. The utility hose, will be solid yellow with a black stripe. All hoses designed for R-134a use will be marked SAE J2196/R-134a. ONLY R-134A HOSES HAVE A BLACK STRIPE.

Service Hose Fittings

Different service hose fittings have been specified by SAE to prevent the mixing of R-12 and R-134a during service operations. SAE J2197 standard specifies that R-134a service hose fittings to have a 1/2 inch, 16 ACME thread for connection to manifold gauge sets or to recovery/recycling/charging equipment. While the R-12 hose fittings are 7/16 inch, 20 thread for connection to the manifold gauge set or recovery/recycling/charging equipment.

The service hose ends that connect to the motor vehicle air conditioning system are also different for R-134a and R-12. This is regulated by SAE standard J639. R-12 service fittings which connect to the vehicles air conditioning system are threaded fittings for both the low and high sides of the system. R-134a systems use a SAE approved quick-connect that doesn't have external threads, which couples the service hose to the vehicle. To avoid confusing the low side from the high side service fitting, the high side R-134a fitting has a 16 mm Outside Diameter, (OD), and the low side fitting has a 13 mm OD.

Safety Precautions

1. Always wear protective goggles when working with refrigerant. If liquid refrigerant gets in your eye, permanent blindness may result.
2. Do not allow refrigerant to come in contact with your skin. The refrigerant has a very low boiling point, which will cause frostbite.
3. All refrigerant handling, charging, and recycling operations should be performed in locations with adequate ventilation of at least four air changes per hour. Avoid prolonged breathing of the vapor. Prolonged inhalation of refrigerant is extremely dangerous; death can occur without warning.
4. Do not use the recovery unit in the vicinity of spilled or open containers of gasoline, thinners, or any other flammable liquid or vapor unless your equipment is expressly designed, (explosion proof designs), for such environments. Do not operate where flammable vapor is present.
5. Do not leave any recovery or recycling machine on and unsupervised.
6. Do not attempt to fill any vessels, containers, cylinders, charging equipment, or storage tanks that are not DOT-approved and equipped with a safety-vent valve.
7. Do not transfer refrigerant to non-refillable cylinders.
8. Do not fill any storage tank or vessel with refrigerant beyond 80% of its capacity.
9. The internal pressure of a cylinder with one ounce of liquid refrigerant is the same pressure as a full cylinder. The explosive damage potential of a cylinder of liquid refrigerant is much worse than a cylinder of compressed air at the same pressure. This is because unlike the compressed air pressure which will quickly drop, the saturated liquid refrigerant will boil-off from liquid to vapor and maintain the high pressure until all the refrigerant is vaporized. You have all experienced the boil-off from a car radiator as the cap is removed. The pressure is only about 15 psig, but it maintains that pressure until essentially all the water in the radiator has boiled off. Imagine that same process occurring at over 100 psig, and with very cold liquid refrigerant which can cause eye damage, frostbite, and skin cold-burns - now you have the idea.

Cylinder Inspection

Prior to filling, a cylinder should be inspected for signs of damage, such as dents or corrosion. Do not fill a damaged cylinder. A recovery cylinder should not be filled if the present date is more than five years past the test date that is stamped on the shoulder of the cylinder. The test date will look similar to the example below:

A1

12        89

23

The designation in the example above indicates that the cylinder was re-tested in December 1989 by re-tester number A123. If a cylinder is out of date, it must not be filled; promptly return it to the cylinder owner for re-testing by an approved test laboratory. As stated earlier in this course, liquid refrigerant will expand as its temperature increases. If the cylinder is overfilled, thermal expansion of the liquid could rupture the cylinder. After filling, it is important to verify that all cylinder valves are closed properly and capped; this will prevent leaks during subsequent handling and shipment.

Review Topics

- The system vacuum level is measured with the system isolated.

- Always isolate the system and relieve the vacuum on the vacuum pump (by loosening the hose connections), for example, before turning the pump off. Otherwise, vacuum pump oil may be sucked out of the vacuum pump and into the lines or system. Vacuum pump oil may not be compatible with the MVAC system's oil.

- During dehydration of a refrigeration system, the refrigeration system can be heated to decrease dehydration time.

- Whenever a technician is working with any unknown solvents, chemicals, or refrigerants, the technician should always review the material safety data sheets, which by law should be shipped by the manufacturer with these compounds.

- Refrigerant vapors or mist in high concentrations should not be inhaled because they have been demonstrated to cause heart irregularities or unconsciousness in some people. Note the warnings on the packaging. Refrigerants are also heavier than air and can displace the air in a room, leaving no breathing air in the room (leading to asphyxia). In most refrigerant accidents where death occurs, the major cause is oxygen deprivation.

- When corrosion build up is found within the body of a relief valve, the valve must be replaced, NOT repaired.

- Never use oxygen or compressed air to leak-check hardware because some refrigerants, when mixed with air or oxygen, can explode. The oil present in shop air, (even in small concentrations), will also contaminate the system.

- The MOST IMPORTANT reason why one should NEVER heat a refrigerant storage or recovery tank with an open flame is that the tank may explode, seriously injuring people in the vicinity.

- When filling a graduated charging cylinder, refrigerant that is vented off the top of the cylinder must be recovered.

- If a large leak of refrigerant occurs, such as from a filled cylinder in an enclosed area, and no self-contained breathing apparatus is available, then the area should be vacated and ventilated.

- When first inspecting a system known to be leaking, you should look for traces of oil because this is an excellent indication of leaks.

- The rotating shaft seal on an open-type automotive compressor is likely to leak if the unit is not used for several months.

- If a system is opened for servicing, the filter drier should always be replaced.

- Non-condensables in a refrigeration system result in a higher discharge pressure.

- Every refrigerating system and refrigerant cylinder must be protected by a pressure-relief device.

- All devices used for refrigerant recovery must meet EPA standards.

- Hygroscopic means affinity for water, so hygroscopic oils are oils with a high affinity for water. POE and PAG oils are hygroscopic oils.

- Recycling is defined as the cleaning of refrigerant for reuse by oil separation, non-condensable gas removal and single or multiple passes through filter/moisture absorption devices.

- Reclamation is defined as processing refrigerant to a level equal to new product specifications as determined by chemical analysis, (testing to ARI 700).

- Recovery is defined as transferring refrigerant in any condition from a system to a storage container without testing or purifying the refrigerant in any way.

- When addressing consumer complaints regarding additional service expense due to recovery efforts, the technician needs to explain to the customer that recovery is necessary to protect human health and the environment. Explain to the customer that recovery is required by federal law, remind the customer that all professional service personnel are duty-bound to follow the law and protect the environment. Point out that there are substantial fines of $27,500/occurrence/day for anyone venting refrigerant.

- When recovering refrigerant, it is important not to mix different refrigerants because the mixture will be impossible to reclaim. In cases where the refrigerant cannot be reclaimed, it must be destroyed. Only one refrigerant type can be recovered into a cylinder at a time.

- A system is not evacuated until a vacuum gauge shows that you have reached and HELD the required finished vacuum.

- After completing the transfer of liquid refrigerant between the recovery unit and the refrigeration system, you must be careful to avoid trapping liquid refrigerant between service valves of the refrigerant hose because pressure can build up in the line and burst the hose.

- All refrigerant tanks, including recovery tanks, should be labeled to indicate their contents.

- A refillable refrigerant cylinder must not be filled above 80% of the cylinders rated volume.

- Removal of the refrigerant charge from a system can be conducted more quickly by cooling the recovery tank.

- Recycling or recovery equipment that use hermetic compressors have the potential to overheat when drawing deep vacuums because the compressor motor relies on the flow of refrigerant through the compressor for cooling.

- After reaching the required recovery vacuum on an system, you should turn off the recovery device, (isolate the system), and wait for a few minutes to see if the system pressure rises, indicating that there is either refrigerant in liquid form, refrigerant trapped in the oil, or a leak in the system.

- Non-condensables in a refrigeration system result in a higher discharge pressure.

Section III Table of Contents