Combines retrofiting R12 to 134a on l3 Gleaner

I just went to a GM A_C service and retrofit class for 2 days.DONT USE ESTER OIl! Ester will not mix with the mineral oil in current r12 system.Use PAG OIl ONlY.PAG will mix with mineral oil already in system.Iusually change receiver drier during retro new drier should have instructions on how much oil to add to drier. shouldnt need to flush system as long as compressor didnt come appart.hope im not to late. good luck.

I would double check your notes on which oil will mix with mineral oil. You have it backwards from what I remember. I've been using ester in the old R12 systems for years with no problems. The retro kits that I have seen have ester in them. I've been told that the ester will mix with either Pag or the old mineral oil.