I was in the auto air conditioning business for 28 years and what you say is true accept that you could actually drop in 134-a to replace R-12 and have decent results. What did happen though was the heat exchangers were improved considerably. And some design changes were made to utilize low pressure / low temperature gasses to lower head pressure by running the high pressure liquid gas through the suction lines.
I was in the auto air conditioning business for 28 years and what you say is true accept that you could actually drop in 134-a to replace R-12 and have decent results. What did happen though was the heat exchangers were improved considerably. And some design changes were made to utilize low pressure / low temperature gasses to lower head pressure by running the high pressure liquid gas through the suction lines.