I just talked to a friend of mine this evening. He told me that one of his buddies put motor oil in his new automotive a/c compressor. The man apparently had past problems with lubrication in his R134a system.
From what I've been told, it's been several weeks since the man used motor oil in his a/c compressor, and the system still works very well.
The man used straight 20 weight non detergent motor oil.
Any thoughts as to how/why this is working?