quite a number of gasses will deliver some form of the refrigeration cycle (it's just an exercise in Boyles' Law, after all). Finding ones that will evap and co

quite a number of gasses will deliver some form of the refrigeration cycle (it's just an exercise in Boyles' Law, after all). Finding ones that will evap and condense at the same pressures (temperatures) as R12 are few, and those that will carry the lubricants needed to preserve the compressor are now quite few in number. R134a is a suitable alternative with only a small decrease in cooling performance. But getting back to your original point, yes you can change the refrigerant gas to almost any arbitrary gas, however, you'll need to change out the compressor, expansion valve or metering orifice and change the condensor & evaporator -- basically completely reengineer the system to match the operating pressures of the new gas. That being said: I would STRONGLY advice against using pressurized flammable gasses in an automotive refrigerant system. You state that "leaks are a concern" but I think that's an understatement better summarized as "dying in a fire due to an otherwise survivable collision is a concern." In an automobile crash an uncontrolled release could occur into the close passenger compartment. Propane is a "poor man's gas", indeed. And a foolish man's. source : I'm a residential HVAC tech