Originally Posted by MarkwithaK
I have to respectfully disagree with this. The oil in 134A is not compatible with the oil used in R-12 and therefor all components should be replaced. That would include the compressor as it was specifically designed to function based on the properties......
While your approach is certainly effective, its very conservative and wholly unnecessary on a system that was in decent shape prior to conversion.
I have converted several older systems quite sucessfully without changing compressors (but they were functioning normally before conversion.)
I never suggested the proper oil should not be added to the system in the proper amounts, but leaving some old R12 type oil in the system is not automatically bad, if the amount is not excessive.