Preface Table of Contents Section II
In 1928, C. F. Kettering, a vice president of General Motors, decided that the refrigeration industry needed a new refrigerant if they ever expected to get anywhere. He asked Thomas Midgely to see if he could find one. Three days after getting the assignment, Midgely and his associates had synthesized dichlorodifluoromethane (CFC-12) and demonstrated that it was nonflammable and had unusually low toxicity. With this development, the fluorocarbon refrigerant industry was born, and rapid expansion of refrigeration and air conditioning was made possible.
Most refrigerants in current use are compounds containing carbon, fluorine, usually chlorine, and sometimes hydrogen, bromine, or iodine. When a refrigerant is referred to as a CFC, the refrigerant contains Chlorine, Fluorine, and Carbon. When a refrigerant is referred to as a HCFC, the refrigerant contains Hydrogen, Chlorine, Fluorine, and Carbon. When a refrigerant is referred to as a HFC, the refrigerant contains Hydrogen, Fluorine, and Carbon.
The refrigerants heard about the most are the chlorofluorocarbons (CFCs). As the name says, these refrigerants consist of chlorine, fluorine, and carbon, thus the abbreviation CFC. Because they contain no hydrogen, CFCs are chemically very stable, even when released into the atmosphere. Because they contain chlorine, CFCs are damaging to the stratospheric ozone layer high above the Earth's surface. The ozone layer is what shields us from excessive ultraviolet solar radiation. The combination of these two characteristics gives CFC refrigerants a high ozone-depletion potential, (ODP), and has made these refrigerants the target of legislation that will reduce their availability and use. Their manufacture was discontinued as of January 1, 1996! R-12 is a CFC and often referred to as CFC-12.
A second category of refrigerants currently available are the hydrochloro-fluorocarbons (HCFCs). Although they contain chlorine, which is damaging to the ozone layer, they also contain hydrogen, which makes them chemically less stable once they enter the atmosphere. These refrigerants, decompose when released in the lower atmosphere so very little ever reaches the ozone layer. The HCFCs therefore have a lower ozone-depletion potential, (ODP). HCFC-22, also known as R-22, has been in widespread use for many years in building and window air conditioning units.
Hydrofluorocarbon (HFC) refrigerants, which contain no chlorine at all, have been developed. These refrigerants have an ozone-depletion potential of zero but probably still contribute to the global warming problem. One new HFC that is replacing CFC-12 is HFC-134a, (1,1,1,2-Tetrafluoroethane CF3CH2F).
Serious concerns involving depletion of the Earth's protective stratospheric ozone layer and the effects of CFC's on this depletion resulted in the phasing out of the production of all CFC refrigerants such as R-12 by January 1, 1996. Recent ozone depletion studies indicate that the current situation is far worse than originally thought.
Key considerations for any new refrigerant are chemical stability in the system, toxicity, flammability, thermal characteristics, efficiency, ease of detection when searching for leaks, environmental effects, compatibility with system materials, compatibility with lubricants, and cost. In general, HFC-134a has replaced CFC-12 in all automotive applications.
HFCs such as R-134a, do not lead to ozone depletion but do contribute to global warming due to the greenhouse effect, so refrigerant recovery and recycling are here to stay, regardless of the new refrigerants developed. Recycling also makes sense economically because of the cost of the new refrigerants and the taxes on the more traditional refrigerants. Since as early as 1992, automotive air conditioning has been using HFC-134a instead of CFC-12.
There are no “drop-in” substitute refrigerants for any equipment category. This means that some changes in a system's equipment or materials of construction are always necessary when converting to a replacement refrigerant. The existing refrigerant cannot simply be removed from a system and replaced with another refrigerant. Usually the changes amount to replacement of incompatible seals and changes in lubricant. Filter-driers, compressors, and seals that are compatible with CFCs, HCFCs, HFCs and their oils are currently being developed; however, the replacements are not without problems. The new (POE), synthetic oils being used with HFC refrigerants are incompatible with as little as 1% residual oil, (PAG or traditional mineral), in the system.
NOTE: HFC-134a still carries some concern about compatible lubricants. Lubricants typically used with CFC-12 do not mix with HFC-134a. Polyalkylene glycols (PAGs) mix properly with 134a at low temperatures but have upper-temperature problems, as well as incompatibility with aluminum bearings and polyester hermetic motor insulation. Ester-based synthetic, (POE), lubricants for HFC-134a resolve these problems but are incompatible with existing PAG or mineral oils.
The thermodynamic properties of HFC-134a are similar to CFC-12, and with proper equipment redesign, efficiencies will be similar. In automotive applications, capacity suffers only minor reductions.
Refrigerants are usually packaged in disposable containers for use by air conditioning and refrigeration service personnel. Disposables are manufactured in sizes from 1 to 50 pound capacities and should never be refilled. Refrigerant manufacturers and packagers voluntarily color code cylinders for their refrigeration products. The color code for R-12 is white and R-134a is light blue.
Disposable cylinders are manufactured to specifications established by the U.S. Department of Transportation (D.O.T). The DOT has regulatory authority over all hazardous materials in commercial transportation. Disposable cylinders manufactured for CFCs are designed to meet or exceed DOT Specification 39.
Transportation of refilled DOT 39 cylinders is illegal and subject to a penalty of up to $25,000 fine and five years imprisonment. The use of a refilled DOT 39 cylinder also violates OSHA workplace regulations and may also violate state laws.
Every cylinder is equipped with a safety-relief device that will vent pressure from the cylinder before it reaches the rupture point. Cylinders can become over-pressurized for several reasons; however, the primary cause is overheating. When temperatures increase, the liquid refrigerant expands into the vapor space above the liquid causing the pressure to rise gradually as long as a vapor space is available for expansion. However, if no vapor space is available due to an overfilled cylinder (and no pressure-relief valve is available), the liquid will continue to expand with no room for the expanding liquid and will result in the cylinder rupturing. When the cylinder ruptures, the pressure drop causes the liquid refrigerant to flash into vapor and sustains the explosive behavior of the rupture until all the liquid is vaporized. The rupture of a refrigerant cylinder containing liquid refrigerant that flashes into vapor is far worse than the rupture of a compressed-air cylinder of the same pressure.
Disposable cylinders are manufactured from steel. Rust can eventually weaken the cylinder to the point where the wall can no longer contain the compressed refrigerant. Cylinders must be stored and transported in dry environments. Cylinders exhibiting extreme rust should be emptied of contents and properly discarded.
Empty disposable cylinders should be emptied (recover refrigerant until pressure has been reduced to a vacuum). The container's valve can be closed at this time and the container marked empty. The container is ready for disposal. We recommend (however it is not required by the EPA of Section 609 technicians), that the cylinder valve should then be opened to allow air to enter, and the cylinder should be rendered useless (with the valve still open) by breaking off the valve or puncturing the container. This will avoid misuse of the container by untrained individuals. Used cylinders can be recycled with other scrap metal. Never leave used cylinders with residual refrigerant outdoors where the cylinder can rust. The internal pressure of a cylinder with one ounce of liquid refrigerant is exactly the same as a full cylinder. An abandoned cylinder will eventually deteriorate and potentially explode.
Refillable cylinders, also referred to as recovery cylinders or recovery tanks, are now available for the transportation of refrigerants used in the air conditioning and refrigeration industry. These refillable cylinders are used for the same refrigerants as are the disposable cylinders. In addition to the disposable and returnable cylinders, refillables also are regulated in their design, fabrication, and testing by DOT for use in the transportation of refrigerants.
Recovery cylinders are painted yellow in the shoulder area and 12 inches down the side. The remainder of the cylinder body is painted gray by the manufacturer. However, we recommend that a color-strip, be painted on the tank, in accordance with the color-coding convention for new refrigerant cylinders, (White for R-12; Light Blue for R-134a), to indicate the type of recovered refrigerant being stored in the tank and to minimize the potential for accidental refrigerant mixing. For refrigeration technicians using recycling machines, we further suggest that the refrigeration technician utilize a "CLEAN" recovery tank for recycled refrigerant and a "DIRTY" recovery tank for recovered, but not recycled refrigerant. Marking the recovery tanks as clean and dirty will avoid contamination of otherwise clean refrigerant by putting clean refrigerant into a recovery tank that once held dirty refrigerant. With the rising cost of refrigerant, the value of the refrigerant stored in a 50-lb. recovery tank is worth five times the cost of a recovery tank. Separating clean and dirty refrigerant will save you money very quickly.
Each cylinder contains a "warning decal" to caution the user against physical contact or exposure to the refrigerant and against using a refrigerant in the cylinder that has a vapor pressure in excess of 318 psig at a temperature of 130°F.
The use of the various refrigerants, in cylinders that are exposed to the environment, is reason for concern, as previously discussed. Although the interior of these cylinders must be void of moisture, the exterior cannot avoid it. Thus, corrosion can and does occur, as well as damage due to mishandling. These are but a few of the reasons why the cylinders must be re-tested at five-year intervals.
The valves should be periodically examined, especially the relief valve. Check to be sure that nothing is obstructing the relief valve and that no visual deterioration or damage has occurred. If any damage is visible, empty the cylinder and have the tank repaired. Never use a cylinder with a faulty pressure-relief valve or with obvious structural impairments. SAE Standard J2296 “Retest of Refrigerant Container” provides the procedure to inspect a refrigerant cylinder used for refrigerant recovery/recycling and charging equipment when servicing mobile air-conditioning (AC) systems.
Careful attention should be given to the following general safety considerations concerning fluorocarbon refrigerants. Before using or handling any refrigerant, personnel should be familiar with safety concerns for the specific product. This is particularly important for some of the new replacement refrigerants for which testing is not yet complete, or long-term health effects are not yet known! Specific product safety information is always available from the manufacturer.
Skin or eye contact with fluorocarbon refrigerants can result in irritation and frostbite. Although the toxicity of traditional fluorocarbon refrigerants is low, (due to their chemical stability), the possibility of injury or death exists in unusual situations or if they are deliberately misused. The vapors are several times heavier than air. Good ventilation must be provided in areas where high concentrations of the heavy vapors might accumulate and exclude oxygen. Inhalation of concentrated refrigerant vapor is dangerous and can be fatal. Exposure to levels of fluorocarbons above the recommended exposure levels can result in loss of concentration and drowsiness. Cases of fatal cardiac arrhythmia have been reported in humans accidentally exposed to high levels. The exposure levels for some of the new replacement refrigerants are lower than for those with which you may be familiar.
If inhaled, the victim should be moved to an area with fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Avoid stimulants. Do not give adrenaline (epinephrine) because this can complicate possible effects on the heart. Call a physician. In the case of eye contact, flush eyes promptly with plenty of water for at least 15 minutes. Call a physician. Flush exposed skin with warm water (not hot) or use other means to warm the skin slowly.
Most halogenated compounds will decompose at high temperatures such as those associated with gas flames or electric heaters. The chemicals that result under these circumstances always include hydrofluoric acid. If the compound contains chlorine, hydrochloric acid will also be formed, and if a source of water, (or oxygen), is present, a smaller amount of phosgene will be formed. Fortunately, the halogen acids have a very sharp, stinging effect on the nose and can be detected by odor at concentrations below their toxic level. These acids serve as warning agents that decomposition has occurred. If they are detected, the area should be evacuated until the air has been cleared of decomposition products. Some other replacement refrigerants have lower exposure limits, so read the manufacturer's warnings carefully and take the precautions seriously.
- Chlorofluorocarbon (CFC) refrigerants are so named because they contain the elements Chlorine, Fluorine, and Carbon.
- CFCs have the highest ozone depletion potential (ODP) and are the most harmful to stratospheric ozone.
- Hydrofluorocarbon (HFC) refrigerants contain Hydrogen, Fluorine, and Carbon. R-134a, also known as HFC-134a, is a chlorine-free refrigerant.
- HFC fluorocarbon refrigerants cause no harm to stratospheric ozone; they have a zero ODP.
- Ester-based synthetic oils cannot be mixed with other oils.
- 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.
- 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.
- A refillable refrigerant cylinder must not be filled above 80% of its full capacity.
- At high temperatures (i.e., open flames, glowing metal surfaces, etc.), CFC-12 can decompose to form hydrochloric and hydrofluoric acids.
- 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.
- Every refrigerant cylinder is protected by some type of pressure relief device.
Preface Table of Contents Section II