Quote:
Originally Posted by jeff5may
Refrigerant grade propane is r290. It has roughly the same pressure range as r22. Butane and isobutane both have lower pressures than r134a. If you are running a txv you'll have to run a blend.
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You are right! Another thing to keep in mind is the maximum pressure that the system is designed to hold. I imagine for a R134A MVAC system the design pressure would probably be about 150-175 PSI on the low side and about 350-400 on the high side, although I'm not sure about those pressures. But if you exceed the maximum pressure that the system is designed for, bad things can happen.
This shouldn't be a problem if you use an R12 or R134A drop in blend or straight R600A, but this CAN be a problem if you blend your own refrigerant, especially if you increase the proportion of propane, the higher pressure gas, or for that matter if you try to use straight propane as some people have suggested to replace R12.
On my car, the pressure relief valve on the back of the compressor looks like it would spray refrigerant right on the exhaust header if it were to blow, which could end badly as is with R134A and oil mixed, but a flammable gas would make that worse.