A3 refrigerants (hydrocarbons) have very low charge quantity limits that basically make them infeasible systems with even modest capacities. Split type air cond

A3 refrigerants (hydrocarbons) have very low charge quantity limits that basically make them infeasible systems with even modest capacities. Split type air conditioners or heat pumps predominately used in the US have several times the allowable limit of charge in the liquid line alone. Building codes have only recently (and incompletely) been revised to allow mildly flammable refrigerants (A2L) inside most buildings for space conditioning. Amending these for A3 refrigerants is an uphill battle. Ammonia is mildly flammable, toxic, and electrically conductive. Good luck finding/building a hermetically sealed compressor that is anywhere near affordable. CO2 in a refrigeration cycle goes transcritical at even moderately warm temperatures, making the system very inefficient without adding several (typically expensive) changes to the cycle. Manufacturers would struggle to build a CO2 air conditioner that meets minimum efficiency standards at anywhere near current equipment costs.