Service Issues


One of the most controversial aspects of A/C service today is compressor lubricants. Because R134a is not compatible with mineral-based compressor oil, it requires a different type of lubricant. Virtually all OEMS today specify one of several different types of PAG oils for their compressors. PAG oils vary according to viscosity, with PAG 46, PAG 100 and PAG 150 being the three most popular blends. The type of PAG oil required depends on the design of the compressor. And because compressor failures are the leading cause of A/C system failures, it is important to use the correct type of lubricant. But technicians are often confused or misinformed about which type of lubricants they should use in various applications.

According to the MACS field study, 53 percent of technicians are using PAG oil with R134a, but 43 percent are using POE (polyester) oil in R134a systems

POE is a popular aftermarket lubricant because it is compatible with both R12 and R134a, making it a good choice for older vehicles that are being retrofitted to R134a. Even so, the "official" MACS and OEM recommendation is to use PAG oil only with R134a. For all newer R134a systems (most 1995 and up vehicles), use the type of PAG oil recommended by the vehicle manufacturer. PAG oil is not compatible with R12 and must not be used in older R12 systems.

Mineral-based compressor oil should only be used in older vehicles with R12. Mineral oil must never be used with R134a because the two will not mix. This will prevent the oil from circulating through the system and lead to compressor failure.

Most replacement compressors today are manufactured with seals that are compatible with both types of refrigerant. But some are shipped dry while others are prefilled with either PAG or POE oil. So installers must be careful to make sure they do not intermix oils or use the wrong type of oil for the application.

Click here to view PAG oil recommendations.

To minimize the risk of a repeat compressor failure, technicians should also do everything they can to protect the new compressor from contaminants. Compressor failures often throw a lot of debris into the condenser, but some of it can also blow back up the suction hose. For this reason, some manufacturers recommend flushing out the condenser and hoses, installing an inline filter to trap debris, and an inlet screen in the suction hose to protect the compressor.

Flushing is also a controversial subject because the vehicle manufacturers do not agree on which technique works best or even if it works at all. Ford approves flushing with VSL338 terpene-based solvent while GM says its okay to flush but only with R134a, no solvents. Chrysler and Toyota do not recommend flushing. If the system is contaminated and contains debris, Chrysler says it is safer to replace the condenser and hoses. Flushing may dislodge most of the debris in a serpentine flow condenser, but does not work very well in parallel flow condensers.

Parts proliferation continues to be an ongoing challenge for the aftermarket. Twenty years ago, there were half a dozen different basic compressor designs. Today the number has grown to over 1800 and will top 2000 before the end of this year!

Refrigerant contamination is another problem the industry faces. In 1997, the MACS field survey found 2.3 percent of A/C systems were contaminated with air, other refrigerants or hydrocarbons. In 2000, the number jumped to 5.3 percent. This underscores the need for shops to use refrigerant identifier equipment do check vehicles prior to servicing them. MACS says 71 percent of their member shops are now using an identifier to prevent cross-contamination.


Not all PAGs are Created Equal
The unique, patented, double “end-capped” formula of PAG provides exceptional chemical stability to the oil. Ordinary PAG is still chemically active while “end-capped” PAG is chemically inactive or stable. Even at high temperatures, the “end-capped” PAG is very tolerant of moisture and will not react to form harmful acids. The bottom chart depicts the vast differences in the wear characteristics between “end-capped” and ordinary PAG

PAG is the Original Equipment Manufacturer’s Choice for Factory Fill
The automobile and compressor manufacturers tested both PAG and Ester Oils. After extensive testing, 100% have chosen to use PAG over Ester for factory fill. All of these manufacturers made this choice with the knowledge that the premium PAG oil cost more than the cheaper Esters.

PAG is the Original Manufacturers Choice for Retrofit
General Motors, Ford, Chrysler, Honda, Toyota, Mercedes, Nissan, BMW, Audi, among others, and all compressor manufacturers recommend PAG as the choice for retrofitting cars from R12 to R134a.

Esters do not Compare in Performance
Chemical stability and wear-resistance are the two major areas of performance difference. When exposed to high levels of moisture and heat, POE (Ester) may undergo hydrolysis, causing it to revert back to its original components of acid and alcohol. The table at the bottom of the page depicts the drastic differences in wear between Ester and “end-capped” PAG.

100% Compatibility with R12 or R134a and Residual Mineral Oil
Double “end-capped” PAG is compatible with both R12 and R134a and can be used in either application (even with residual oil). Ordinary PAG should not be used in the presence of R12.

3 Viscosities (46, 100 and 150)
Compressor manufacturers use different viscosity PAGs to help lubricate under different conditions. Most compressor parts are now aluminum and the new style compressors, such as rotary and scroll, are more sensitive requiring maximum lubrication to function for extended periods. A single viscosity “universal” Ester or PAG is not recommended for maximum service life.

Compressor Manufacturer approvals:
Calsonic Harrison, Denso (Nippondenso), Ford, Halla Climate Control, Sanden, Seiko Seik, Seltec (Tama) and Zexel have approved double “end-capped” PAG.

Note. The standard SAE test was conducted using an aluminum pin rotating between two aluminum blocks. It has been modified to control specific parameters including temperature, pressure and atmosphere (air, R134a, R12) to simulate actual conditions within a compressor.


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