Avoiding an oily situation

By Richard Hawkins, MACS Contributor

Some parts of the country are starting to see warm weather and air conditioning season is just around the corner.  If you own a mobile A/C repair shop this is when you start to gear up for it, by replenishing your parts inventories and an important segment of those inventories is compressor oil.

Compressor oil:  A short history

With all the different compressors that are in use and all the different oils on the market, having the correct oil on hand is much more challenging that it used to be.  Back in the “Good Old Days” of R-12, there were two viscosities of mineral oil that were commonly used and then a third mineral oil with a paraffin additive came along in the late 1980’s.

In the early 1990’s, R-134a was introduced to the marketplace and all the OEMs started using PAGS of several different viscosities with it. Then retrofitting became a big thing (for several years) and a lot of oil companies were pushing POE (Ester).  Along the way, some aftermarket companies introduced PAO (Poly-alpha-olefin).  Then Hyundai/Kia decided to use PVE (Poly-vinyl- ether) as an OEM oil in some applications.

 While all this was going on, the use of electric compressors (in hybrid and electric vehicles) was increasing and most OEMs selected POE, but it was a different POE from that used in retrofitting.   Then R-1234yf was introduced into the marketplace and most OEMs chose PAG for vehicles with belt driven compressors and most chose POE for electric compressors.  To complicate things a bit more, these PAGs and POEs were different from that which had been used with R-134a. Since the days of R-12, the selection of oils used for mobile air conditioning has morphed from one type and two viscosities to four types and over a half dozen viscosities.

Oil selection tips

PAG 46, 100 and 150 are the viscosities that are commonly encountered in the aftermarket, but in the OEM world there is also 56, 68, 125, 133 and maybe some more I have not heard of.   The aftermarket has been able to cover these additional viscosities with the three standard viscosities, but some companies have taken this a step further by offering some “universal” oils which typically have a viscosity somewhere between 46 and 100. It can be tempting to reduce inventory levels by stocking and using universal oil, but it is best to make sure that your compressor suppliers accept the use of it first, so that you do not get into any warranty issues. 

It is important be aware that a compressor such as a A-6 or R-4 which requires a high viscosity oil (PAG 150) may have an unacceptable noise level if operated with “universal” oil due to the viscosity being so much lower.

Note: There are aluminum body A-6 replacement compressors and scroll style replacement R-4 compressors which are not designed for PAG 150 which this would not apply to.

It is more complicated than it used to be

Another thing to also keep in mind also is that if you are servicing vehicles that use R-1234yf refrigerant, the oils they use contain acid reducing additives.  So even though a given R-1234yf vehicle might use PAG 46, older PAG 46 that is for R-134a systems should not be used.  Most manufacturers have indicated that the R-1234yf PAGs are backwards compatible for use with R-134a systems, but the R-134a oils are not forward compatible with R-1234yf systems.

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