Using Forane^® R-134a Refrigerant

Automotive air conditioners, also known as mobile air conditioners (MACs), though small in size, do not lack in complexity. Several issues that should be addressed when retrofitting MACs are: elastomers (O-rings and hoses), oils, compatibility with residual mineral oil and R-12, dryers/desiccants, and performance. Arkema has addressed most of these issues in the extensive testing done with its retrofitted fleets and has concluded that 134a retrofitting, while a challenging project, can usually be completed very cost effectively and with little time or effort.

Regarding the refrigerant choice for a retrofit, overwhelmingly, the mobile air-conditioning industry has selected HFC 134a as the refrigerant of choice and Arkema fully supports this position. However, while HFC 134a is the only pure refrigerant available, there are several other candidates in the market in the form of blends. Some of these blends may be flammable, and service technicians should be aware of them to avoid possible cross contamination or safety hazards involving their equipment. Although many of these blends have been approved for use in automobiles by the EPA, there may be several problems associated with blended refrigerants in a MAC retrofit. Due to the chemical makeup of the blend, there may be compatibility problems with the elastomers (O-rings, seals, etc.) and hoses used in a MAC system. These compatibility problems may cause refrigerant leaks and, in some cases, system failure.

Arkema has conducted extensive research on several key issues that affect R-134a MAC retrofits. Elastomers, while still needing to be checked for material compatibility, did not display any special problems in the vehicles Arkema converted. The leak rate per year was approximately the same once the system was thoroughly leak tested and retrofitted over to R-134a. Most R-12 elastomers are compatible with R-134a and the newer oils it requires.

For lubricant oils, there are currently two choices of synthetic materials: Poly Alkaline Glycols (PAGs) and Polyolesters (POEs). Although the choice varies with the car manufacturer, most have chosen PAGs as their Original Equipment Manufacturer's (OEM) fluid, and their retrofit fluid. However, sometimes a manufacturer may recommend the use of a PAG for OEM and POE for retrofits. Our studies showed no differences in performance or operating conditions when using either PAG or POE oils. Be sure to check with the vehicle manufacturer for any retrofit oil specifications. If no particular oil is specified for retrofits, use the oil recommended by the OEM for their new R-134a systems.

There have been many developments in the last few years regarding the specific procedures for retrofitting when it comes to removing the old mineral oil in the systems. Contrary to other information, PAG and POE are both compatible with mineral oil. Many OEMs are recommending that the old mineral oil be left in a system after removal of the R-12. Because HFC-134a will not mix with mineral oil, it is critical that an additional charge of PAG or POE (check with OEM guidelines) be added to the system for proper compressor lubrication. The amount of oil may decrease refrigerant charge since the system will contain twice the original oil charge. Because R-134a refrigerant is not as dense as R-12, it generally requires between 85-90% by weight of the original R-12 charge. Check with OEM recommendations for proper charge amounts.

Extensive research and field study has shown that most desiccant currently used in R-12 systems is suitable for use with R-134a. As the desiccant/dryer bags (located in the accumulator or receivers in systems) age, they eventually fill with water and will not continue to remove moisture from the system. Most OEMs recommend changing out the accumulator/dryers on older or high mileage vehicles and on systems that have been open to the atmosphere for extended periods of time. Follow the recommended OEM guidelines on dryer/desiccant change outs.

Arkema, while converting its fleet, chose not to replace any system components other than what was necessary to eliminate compatibility problems. The cooling performance observed with our R-134a retrofitted test fleets was equal to what was experienced previously with R-12. Some OEM guidelines may recommend certain system component change outs or additions such as larger capacity condensers to achieve the level of performance that equals or exceeds R-12. The level of performance you or your customers expect from your system may affect how extensive and costly a retrofit you may need to undertake.

All refrigerant and system handling regulations that apply to stationary air conditioning and refrigeration units, also apply to MACs. In addition, a set of Society of Automotive Engineers (SAE) J-standards specific to mobile applications also apply. One of the most important standards deals with the retrofitting of the service ports. Typically, MACs have two service ports, one on each side of the system. The high side is a 3/8" and the low side is a standard 7/16" refrigeration flare fitting, both with external threads. After a system retrofit to HFC-134a is completed, these fittings must be changed to Forane^® 134a approved fittings per SAE J-639 (internal, metric threads) in such a way that the CFC-12 original fittings are permanently disabled.

In summary, retrofitting to R-134a refrigerant in most cases can be done very easily and cost effectively. Removing the old mineral oil from the system is not always essential. As long as you add the new PAG or POE oil, proper oil return can be expected. Depending on the level of system performance you or your customers expect, R-134a retrofitting can be accomplished on most vehicles with little if any system changes. Remember, always consult the vehicle manufacturer for any specific guidelines they may have.