Ford Repair: 1989 Taurus r-12 vs r-134a, r 134a, ford taurus

Question
If the system is evacuated but no other changes made, can you replace r-12 with r-134a in a 1989 Ford Taurus?

Answer
No. There will always be oil in the system, and as much of the oil as possible should be removed. Usually replacing the accumulator will get rid of most of it, as well as flushing the system and for best performance changing the oil in the compressor. You can replace r-12 with r-134, but most likely this will just cause other problems later.
The r-12 mineral oil is not compatible with r-134.