Well . . . That was THEN . . . THIS is NOW ! ! !
If you have a supply of R-12 that was purchased back when it was a BUCK a POUND . . . GO FOR IT ! ! ! Being in some areas, it now goes for 100 BUCKS a POUND . . . R-134A is the ticket.
In the REAL WORLD . . . R-134A WORKS as an SAE and DOT APPROVED refrigerant.
There are a couple of guys a few miles away from here who are doing 10 years for charging systems with Butane. I was one of the FIRST shops in my area to retrofit to R-134A . . . You wouldn't believe the BULL**** that I heard from people who didn't know **** from Shine-ola. There were shops who were just adding R-134A WITHOUT doing ANYTHING ELSE . . . Compressors were locking up INSTANTLY and R-134A was the SOLE BLAME. These were the same IDIOTS who told people NOT to go to my shop as I CEASED using R-12 due to COST and was ONLY retrofitting to R-134A.
I have a retrofitting formula that I've developed from utilizing the BEST retrofitting procedures from various sources. I've been retrofitting for over 11 years with no MAJOR complaints.