You'll get all manner of responses, opinions, and commentaries on this matter. First make sure it's actually legal to use it, many hydrocarbon-based refrigerants aren't actually permitted for use in cars. It almost certainly won't last as long as R12 in a well-sealed system because relatively speaking, R12 is made up of big molecules. Same reason R134a bleeds out faster. And many people report failed compressors following refrigerant changes, but I suspect that's got more to do with putting a component back in service after it's been sitting idle for months or years at a time - a dried-out compressor seal that hasn't held pressure for a while is bound to fail shortly after being put back in use (hence the importance of cycling the a/c once in a while even in winter). And it's not as simple as topping up the R12 with substitute - the system must be evacuated completely first. If you know you've got a tight system that's holding pressure and you've been using it until recently I'd probably stick with R12, it's expensive but it works well. This could be the time to look at R134a, too, but if you'll just need a little R12 to supplement the existing charge that'll be recovered from the system, stay R12. FWIW I am considering an R12 substitute for my 740, only because it's currently cheaper than R134a here, and the system has been opened and not used for a while, I expect something to fail anyhow when I charge & use it.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina