A major thing folks forget when discussing refrigerator and AC units is that the EPA has been forcing a phase out of various refrigerants. Good old Freon was great stuff, would run forever at fairly low pressures. Unfortunately it chewed a hole in the ozone when released. The various replacements require higher pressures and that makes things more difficult for longevity. I don't even know what the current brew is but recently read that its being phased out and replaced with another version with even lower ozone depletion potential.
If not for the challenge of the high pressures required and others, we'd probably be using CO2 for a hundred years by now. But it seems to be gaining ground now commercially and will likely continue to become mainstream.