Which Oil to Use with R-134a? - Automotive Air Conditioning

Question:  With so many oils available, which one should I use?  Is there a good universal oil?

You should use the oil that matches the recommendation by the original manufacturer.  We don't believe in a one size fits all compressor oil.  Internal clearances and oil return are factors that change with each system.  Based on testing, compressor manufacturers select the oil that offers the best protection for their particular design. 

We know most shops don't like to stock all the different oils, and technicians often have a hard time determining which oil should be used in each system.

Here's some tips to get you going in the right direction. 

First...  Deciding which oils to keep in inventory isn't difficult, especially since most of the vehicles we work on are now R134a equipped.  When R-134a replaced R-12, PAG became the factory specified oil.

You'll find three common viscosities when choosing PAG oil. 

• PAG (ISO) 46 - Thin
• PAG (ISO) 100 - Medium
• PAG (ISO) 150 - Thick

GM sometimes recommends oil which is close to ISO 135.  In this case, PAG 150 is generally accepted by most technicians.  We've had reports that ESTER oil used in GM compressors that specify ISO 135 may experience unusual knocking sounds.  Most Ester oils have a viscosity closer to ISO 100.   

Second...  Keep an oil chart and specification guide close at hand.  It's useful to have around when trying to figure out which oil goes where.

We are working on our refrigerant oil chart and should have that available as a reference here in time for A/C season.