|Automotive Air Conditioning Retrofitting|
|Table of Contents|
|CFC-12 (R12) has been used in cars to let us enjoy a cooler environment on those hot summer days for many years.
In the 70's scientists discovered a hole in the Ozone Layer, and attributed this damage mainly to the use of chloroflourocarbons, which includes CFC-12 used in Automotive Air Conditioning systems.
What is the Ozone?
The Ozone is the atmospheric layer which protects us from the suns harmful Ultraviolet rays, and also maintains a climate suitable for human habitation on the earth. Without it we'd all perish. Over the past few decades, it has been discovered that that certain area of the ozone layer have been compromised. Scientists feel this this damage has been caused in part by chloroflourcarbons, including the chemicals used in mobile air conditioning systems. As a result, recent studies have shown an increase of UV "B" radiation caused by this damage to the ozone layer. If this damage continues, an increase of certain cancers, including skin cancer, cataracts, and reduced crop may result.
Introduced in a worldwide meeting, the Montreal Protocol which is an agreement between 24 countries, to reduce CFC production to 50% of the 1986 amounts by 1988. Since 1987, membership in the Montreal Protocol has increased to over 132 countries. In 1990 this conglomeration called for a CFC phase out by the year 2000.
Additionally, in 1990 the United States Congress, fully supporting the Montreal Protocol, amended the United States Clean Air Act to control production and use of refrigerants needed for all applications, including but not limited to Automotive applications.
In 1992 President George Bush ordered a halt in the production of all CFC's by December 31, 1995. After which time, no CFC's can be produced or imported into the United States. This left the US with only inventoried and recovered CFC's for use. The Clean Air Act also implemented an escalating (increasing) tax to be applied to the purchase of CFC's. The result being the high cost of R-12 in the past few years.
Efforts to cope with this ultimate demise of CFC's resulted in many alternate refrigerants containing a vast array of sometimes harmful chemicals to hit the market, advertised as "drop in replacements" for R-12. Currently, there is only one recognized alternative to R-12, HFC-134a, and it is the only refrigerant approved for use by the major car makers.
In 1991, in response to the Clean Air Act and the CFC phase out, manufacturers began to focus their efforts on providing an environmentally friendly alternative to CFC's. They came up with HFC-134a, which contains Hydrogen in place of the chlorine. Additionally, many concerns arose of the effectiveness of converting a previously CFC system to this new refrigerant. We now know this conversion to be a viable alternative in most cases to a CFC based MVAC system. OEM's (Original Equipment Manufacturers) have invested countless hours researching and testing refrigerants and conversion techniques to make a previously R12 system work efficiently with R134a. From this research, OEM's developed specific retrofit kits for converting these systems.
|Retrofitting - What is it?|
|Several SAE (Society of Automotive Engineers) standards define the necessary steps and basic procedures involved in retrofitting MVAC systems. A retrofit in layman's terms is the conversion of a CFC based system to use a HFC refrigerant. With little or no degradation in performance/service life from that of the CFC based system.
Repair vs. Conversion
As long as CFC-12 is available is is legal to service previously CFC-12 bases systems. Once supplies are depleted, the system will have to either be converted to the non-CFC based system, or taken out of service. The extent of the conversion will ultimately depend on the age and condition of the system at the time repair are undergone, and how/where the vehicle is driven. Stop and go driving for example place a high demand on the system and will ultimately affect performance.
|Service with CFC-12 until ???|
|As long as CFC-12 is available, use of it will be at the discretion of the person making the repairs. When the reserves are depleted, the only alternative will be to use alternate refrigerants.
Existing Components and their Compatibility
Now that you understand the history and basic necessities for a successful conversion, lets look at the compatibility or the various components in existing CFC based systems:
Existing expansion devices have shown the ability to accurately meter flow of HFC's after a retrofit. In some cases however, the car manufacturers have recommended expansion devices optimized for use with HFC's to more accurately control flow due to the slightly different cooling characteristics of HFC134a.
Evaporator Pressure Control Valves:
These valves maintain low pressures in the evaporator of approx. 26-30 psi. Since refrigerant temperature is directly related to refrigerant pressure, evaporator temperature can be controlled by evaporator pressure. It has been decided that the existing control valves will provide satisfactory performance, provided it is in good working order.
The existing evaporator core will provide the necessary heat transfer when the system is converted to use with HFC134a, and should only be changed in the case of a leak.
Desiccant and Driers/Accumulators:
The Receiver Dryer/Accumulator will serve the sane purpose in both systems, however the CFC-12 system uses a desiccant named XH-5 and is NOT compatibly with HFC134a. The HFC will actually eat the desiccant bag, releasing the desiccant pellets through the AC system, damaging other components. In the HFC134a system, you must use a XH7 or XH9 type desiccant, which is compatible with both CFC and HFC based refrigerants. As a side note, I believe all driers/accumulators being sold now are crossways compatible.
Several engineering studies indicate that existing CFC-12 compressors performed acceptably when the system was retrofitted with HFC-134a. These studies suggest that previous use had conditioned the inner surfaces of the compressor with a chloride film that helps the compressor tolerate the use of HFC-134a. Therefore it has been indicated that the original compressor should perform satisfactorily with HFC-134a. However, if the original compressor cannot tolerate the higher pressures associated with the use of HFC's, a shortened service life will result. If a compressor change is required it is suggested you install a HFC compatible unit. If one is not available, you might check with the component manufacturer to see which replacement compressor might work satisfactorily in your application.
Systems designed for use with HFC-134a generally implement a condenser with increased efficiency. They are generally a rectangle tube type design, sine a rectangle tube will yield more surface area to expose more refrigerant for heat transfer in the same amount of time. A CFC system with limited condensing capacity will more likely produce higher discharge pressures when converted to HFC-134a, especially at higher ambient temperatures and during idling conditions. A technician will have to determine the appropriate course of action to improve system performance if this problem is observed.
The existing high/low pressure switches should perform satisfactorily in use with HFC-134a. If any of these components has failed or does fail, it is recommended to replace with the HFC-134a compatible versions.
It's important to note that all hoses have differences. Hoses manufacturers use different materials and construction varies by manufacturer as well. Some combinations leak more than others, and may not contain the smaller HFC-134a molecule, resulting is more frequent A/C service. Test results indicate that R-134a leaks through walls of non barrier type hose at a slower rate than originally thought. Apparently the mineral oil absorbed by the hose walls somewhat reduces the size of the pores in the hose, aiding in containment of refrigerant. Hose leakage rates have been shown to decrease with use of the newer synthetic lubricants. What does this mean?? Simply put, if the integrity of the existing hose material and the associated hose couplings are intact, the existing hose may be used. If the hoses are to be replaced due to leakage during service, it is recommended barrier type be used, with the appropriate fittings.
O-rings,Gaskets, and Seals
Heat, operation, and age will take their tolls on sealing. Keep in mind that disturbing o-rings on one side of a component may cause another side to leak. These problems are not new to automotive service. Under normal conditions, it is not necessary to change these components during a retrofit to HFC-134a, unless they are leaking, a component has been replaced, or the manufacturer has determined the sealing material is not compatible with the new refrigerant/oil. The two most common gasket materials found to be compatible with the new refrigerants are: high grade neoprene, and Hydrogenated Nitrile Butadine Rubber (HNBR), and are in use by many automobile A/C manufacturers. To avoid using the wrong seals for an application, it is wise to keep the different variations separated from each other. Additionally the newer type o-rings are usually a different color than normal ones.
The existing ports should be checked for o-ring wear and leakage. It is advisable to change the schraeder valve cores to a type compatible with HFC-134a. New HFC134a service ports will be utilized in a retrofit, and depending on manufacturer design, may or may not use existing schraeder valves to aid in sealing.
Lubricants seem to be an issue of confusion. Mineral oil, which has been used in CFC-12 systems since the dawn of time are NOT compatible with HFC-134a. Two new synthetic oils have been developed for use in HFC based systems. Polyalkaline Glycol (PAG) and Polyol Ester (Ester). Both perform well in HFC systems and are commercially available. It is up to the discretion of the compressor manufacturer or the retrofit kit manufacturer which oil you'll use.
|The EPA keeps a listing of new acceptable refrigerants on their Web site. But they do go on to say that not all of the refrigerants are suitable for use in automotive applications. It is advisable to ask your manufacturer, service technician, or refrigerant manufacturer if the particular refrigerant will work in an application. Be sure the refrigerant you are using is meant to be a substitute for CFC-12 and NOT for HFC-134a, as introducing other refrigerants WILL void any warranty you have, and quite possibly damage the system. Vehicle manufacturers recommend ONLY HFC134a for retrofitting because it is the ONLY refrigerant that meets manufacturers' performance and durability requirements. It is widely available, inexpensive, and you will be able to obtain service on a HFC134a system almost anywhere in the world.
Beware of Flammable Refrigerants
It is ILLEGAL to replace CFC's with a refrigerant consisting of pure propane, butane, or any other flammable substances. Vehicles presently designed for use with CFC-12 should NEVER be repaired with a flammable refrigerant. Think what would happen if you had a evaporator leak and lit a cigarette????
A word on replacements other than HFC-134a
A number of refrigerants other than HFC-134a have been listed by the EPA as acceptable under its Significant New Alternatives Policy (SNAP) program, or are under SNAP review. The SNAP program evaluates substitutes ONLY for their effect on human health and the environment, and not for performance or durability. NONE of these refrigerants have been endorsed by the OEM's for use in motor vehicles, and few have had extensive testing in a wide range of vehicle models. Additionally a problem with using one of these alternatives is that they are not readily available in all parts of the country. While some of these manufacturers of these refrigerants claim they are direct drop ins, there is NO SUCH THING as a refrigerant that can be dropped in place of or along with existing CFC-12. For more information on the SNAP requirements on which alternatives have been reviewed, accepted, or deemed unacceptable by the EPA, call the Ozone Hotline number at 1-800-296-1996 and ask for a copy of "Choosing and Using alternative Refrigerants in Motor Vehicle Air Conditioning".
|The current retrofit procedures:|
|The retrofit basically is a straightforward deal.
|Information gathered by IMACA and EPA. Compiled arranged and written by Jim Testa.
More information can be obtained at the EPA's web site: www.epa.gov
The MACS web site: www.macs.com and the IMACA web site: www.imaca.com