Systems using R12 are/were more efficient than those using R134A. Back in the day when R134A was being introduced, there were at lot of unknowns and opinions about changing systems (automotive) to R134A. In the end it was recognized that all the components could be reused especially the hoses as a “barrier” had formed on the inside of them. Of course, compressor oil had to be changed along with a new filter/drier, and a slight reduction in refrigerant weight/system charge IIRC. Also, at the time it became law (in Canada) that you required a refrigerant technician licence to open, evacuate, and charge automotive systems , and anytime one of the systems had been serviced, a sticker was required denoting date, system charge, etc. You also were not allowed to just “top up” a leaking system, but instead had to evacuate and recycle the refrigerant, find the leak, and fix it. Makes sense really, but lots of folks just “top it up” anyways. What I found interesting at the time while installing some of our rotary vane AC compressors on NYC subway cars which used R22, is that they (NYC Transit) had an exemption, so they could still use R22. They also had lots of refrigerant leaks, and would “top up” systems daily. Was a total joke. Was also told, since refrigerants like R12/22 were excellent degreasers, they were still allowed to use them in the Petro-chemical industry to clean out the massive oil/fuel storage tanks. Lol!