Question: is pag oil compatible with r12?
Answer: R12 systems used mineral oil, but unfortunately mineral oil doesn't dissolve in R134a. So, along with R134a came a new oil: Polyalkylene Glycol—or PAG oil. ... The advantage of ester oil is that it works with both R12 as well as R134a, so you can fill the system with it and then use either refrigerant.