I've been researching which oil to use when I get around to reinstalling my AC components, all of which have been used with 134a only. I understand that POE oil will work fine with R-134. I understand that PAG oil of the right viscosity will also work, and that the new, "double-ended" PAG oils are only minimally hygroscopic. "Single-ended" PAGs seem to both hold and hate water, as well as any other impurities, such as residual mineral oils in retro-fitted systems.
Given PAG's evidently finicky nature -- whether or not it is now tamed -- here is my question: What ADVANTAGE do PAG oils have over POEs? There must be some reason that manufacturers, including Volvo, use PAG as the factory lube in 134a systems, but I haven't been able to find out what it is.
Thanks for any light you can shed.
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jds
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