Currently, there are 3 refrigerant choices I know of: R-12, HC, and R-134A. HC & R-12 work about the same (HC slightly better), and both are better than R-134A. Better means lower max pressure and more efficient. I understand that home refrigerators in Europe have used HC refrigerant for many years. I also wonder why no new cars come with it. Probably due to perceptions, which are hard to change and expensive to overcome. Similar question for coolant like Evans Waterless. I recall that GM did ship cars (Corvette?) with such a coolant years ago, but it confused people. I think many motorcycles come with DOT 5 (silicone) brake fluid, so there are occasional advances.
