> Civil society including especially NGOs, played critical roles at all stages of policy development leading up to the Vienna Conference, the Montreal Protocol, and in assessing compliance afterwards.[64][65][66][67] The major companies claimed that no alternatives to HFC existed.[68] An ozone-safe hydrocarbon refrigerant was developed at a Hamburg technological institute in Germany, and in 1992 came to the attention of the non-governmental organization (NGO) Greenpeace. Greenpeace was given the patent, called it "Greenfreeze," and left the patent as open source.[69][70] The NGO then worked successfully first with a small and struggling company to market an appliance beginning in Europe, then Asia and later Latin America, receiving a 1997 UNEP award.
It describes how well it was adopted worldwide, except for the US, then:
> In the U.S., however, change has been much slower. To some extent, CFCs were being replaced by the less damaging hydrochlorofluorocarbons (HCFCs), although concerns remain regarding HCFCs also. In some applications, hydrofluorocarbons (HFCs) were being used to replace CFCs. HFCs, which contain no chlorine or bromine, do not contribute at all to ozone depletion although they are potent greenhouse gases. The best known of these compounds is probably HFC-134a (R-134a), which in the United States has largely replaced CFC-12 (R-12) in automobile air conditioners. In laboratory analytics (a former "essential" use) the ozone depleting substances can be replaced with various other solvents.[76] Chemical companies like Du Pont, whose representatives even disparaged Greenfreeze as "that German technology," maneuvered the EPA to block the technology in the U.S. until 2011.
There are plenty of good, non CFC refrigerant gases. You just need something that will liquify under moderate pressure. Propane/isobutane (aka camping gas) works, in fact it's a poor-mans gas to use to recharge old R-12 systems in cars that haven't been converted. Unfortunately it's quite flammable so leaks can be a concern.
Others, e.g. ammonia, work well but are toxic.
Good, stable, non-flammable, non-toxic refrigerants are not that common. Some automakers are trying using CO2 but that requires much higher pressures.
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.
> Civil society including especially NGOs, played critical roles at all stages of policy development leading up to the Vienna Conference, the Montreal Protocol, and in assessing compliance afterwards.[64][65][66][67] The major companies claimed that no alternatives to HFC existed.[68] An ozone-safe hydrocarbon refrigerant was developed at a Hamburg technological institute in Germany, and in 1992 came to the attention of the non-governmental organization (NGO) Greenpeace. Greenpeace was given the patent, called it "Greenfreeze," and left the patent as open source.[69][70] The NGO then worked successfully first with a small and struggling company to market an appliance beginning in Europe, then Asia and later Latin America, receiving a 1997 UNEP award.
It describes how well it was adopted worldwide, except for the US, then:
> In the U.S., however, change has been much slower. To some extent, CFCs were being replaced by the less damaging hydrochlorofluorocarbons (HCFCs), although concerns remain regarding HCFCs also. In some applications, hydrofluorocarbons (HFCs) were being used to replace CFCs. HFCs, which contain no chlorine or bromine, do not contribute at all to ozone depletion although they are potent greenhouse gases. The best known of these compounds is probably HFC-134a (R-134a), which in the United States has largely replaced CFC-12 (R-12) in automobile air conditioners. In laboratory analytics (a former "essential" use) the ozone depleting substances can be replaced with various other solvents.[76] Chemical companies like Du Pont, whose representatives even disparaged Greenfreeze as "that German technology," maneuvered the EPA to block the technology in the U.S. until 2011.
0: https://en.wikipedia.org/wiki/Ozone_depletion