PAG vs Ester A/C Lubricants

Just about everything. Lubricity, refrigerant miscibility, compatibility with mineral oil and chloride residue, hygroscopic properties...

Not really, no. There is overlap in their applicability, but it's best to use the type of lubricant specifically called for by the system under repair. What are you trying to do?

DS

In general, when the system calls for PAG, I use PAG. On older systems that started with mineral oil and R-12, I generally flush as much oil out as possible and use ester oil since it is supposed to be "compatible" with mineral oil and 134A. There was a rather detailed article in one of the trade rags a few months ago (might have been Motor Magazine) that detailed all the differences. Maybe you can find that article online somewhere.

Cheers,

C

PAG is a better lubricant than Ester (although not as good as mineral oil, but mineral oil doesn't work with R-134a.). Plain PAG, however, is highly reactive in the presence of chlorine (residue from R-12) and will turn into brown goo. There are stabilized PAG oils on the market ("double-end-capped" PAG) that are supposed to be stable in the presence of chlorine, but I question just how stable they are in the long run. Will they start breaking down after 3 years? 5 years?. PAG oil also absorbs water as readily as brake fluid, and shouldn't be used if stored in an opened container for any length of time. Buy only enough for your immediate needs.

Ester (aka POE) is less reactive and in fact can be used in straight R-12 systems. But of the 3 available oils (PAG, POE, and mineral) it is the poorest lubricant. But, since mediocre oil is better than oil that has been turned to brown goo by chlorine, POE is usually used in R-12 retrofits. It absorbs water also, but to a lesser degree than PAG.

And then there are these newer oils showing up:

(server's down as of 3PM EDT 7/22, but I pulled itup the other day after learning this is what's in my '89 Ram's system) DS