Sigh, so much of this discussion is political.

The "problem" with R12 was that it breaks down in the atmosphere in short order (less than 10 years by some calculations). Most of the replacement refrigerants are basically inert. The estimated lifetime of r134a is 50,000 years. So even tiny leaks over a long period are going to do incredible damage to the climate. This was known from the beginning and is by design (the stable molecule bit).

But even now decades later the political ideology that AC units were the "problem" persists, despite the fact that its well documented that CFC's were used for everything from propellants in consumer products like silly string and hairspray, to large scale industrial uses like popcorn production (again recently in china).

Yet in all this time, we haven't really found a better set of refrigerants.

In the end, we would be better off bringing R12/22/etc back with the stringent controls for licensing/recovery/recycling/leak detection/etc that was put in place when they were banned. Combined with proper systems engineering to avoid leaks that are now required due to the refrigerants being extremely flammable or generally dangerous to human life we would both solve the problems of them being in the atmosphere, while avoiding the engineering problems of designing AC units that have to compress azeotropic compounds to extreme pressures, or function close to their critical points in tropical climates or any number of other problems with lubrication/etc.

I think butane or propane is the standard refrigerant for household refrigerators all over the world nowadays; the US is the odd man out.

R134a is still unfortunately widely used in cars. Newer cars are moving to R1234yf, which is expensive, maybe CO2 in the future.

Mercedes is already doing CO2, and the next-gen EV platforms are going that route as well, from what I hear. The high pressure of CO2 systems mean that they're very compact, and thus much easier to integrate with battery pack temperature regulation, AFAICT.

That's good to hear.

I think the interest for EVs might be due to CO2 systems being capable of working as heat pumps as well, producing hot air. Otherwise you'd waste a lot of electricity in cold climates.

Exactly this, both that they're able to heat the interior of the car, but also that they can play the role of battery cooling system (just heat a small radiator instead of inside of car).

Part of this is the regulation in the US around refrigerant reclamation. Once a gas is used as a refrigerant, it has be reclaimed/recycled or large fines can be assessed, even though the rules do not apply when the same gas is used in any other context.

This makes switching to a new gas much harder as the infrastructure for reclaim/recycle does not exist for the new gas, no mater how safe or better it is.

I wonder if the use of these same gases for canned air is at all significant compared to its use as a refrigerant. Regulators seem not to care if people squirt off KGs of the gas to dust off keyboards!

One very interesting refrigeration cycle I heard about recently is using a proton exchange fuel cell in reverse as a compressor for hydrocarbons or ammonia in a closed loop.

Protons jump across the membrane, creating a small pressure differential that is allegedly big enough to do heat pumping.

Ammonia refrigerators were ones of the first types. And they get very cold, quick.

Of course, when ammonia leaks, it does some nasty damage.