Propane can be used as a refrigerant. It is cheap and performs reasonably well. The obvious downside is flammability. In the US the total charge for a propane f

Propane can be used as a refrigerant. It is cheap and performs reasonably well. The obvious downside is flammability. In the US the total charge for a propane fridge or AC is limited to 150 grams of propane. That is a rather small window unit. I think propane had to wait for precision manufacturing to be commoditized before it could be tolerated in living spaces. Leaking propane around switching electrical equipment can end badly.