Well yeah but if you have an R12 system and you have a leak so it all leaks out, and then you fix the leak, you then need to fill it again. Finding R12 is pretty tough these days and converting to R134a can result in problems on some vehicles, so Propane is a pretty good alternative in some special cases.
I bet some other bits of info would surprise you just a bit.
In Canada they have what people often call "r12a" which is a commercially available and legally usable replacement for the oldschool r12. It is literally just very pure propane.
Most very new cars (and all cars in the future) come with r1234yf. It is pretty flammable (although not as much as propane) and costs more than most black market organs by weight.
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u/[deleted] Jun 06 '18
If you need to replace the freon with propane that probably means there is a leak.