Can you mix R22 and R22a?

Answer 1

In the USA it is unlawful to mix R22 (chlorodifluoromethane) with R22a aka R290 (propane, aka liquiefied petroleum gas) (propane). While the two are not incompatible working fluids mixing them is a bad idea even where it is not unlawful. R290 is a known refrigerant with many excellent properties and one major drawback - flammability. As a practical matter, R22 was created because early air conditioners using ammonia, propane, and other toxic or flammable materials were dangerous when they failed, and air conditioning was not accepted as safe for the home. Propane has not become any less flammable since that time. In the event of a rapid loss of refrigerant (e.g. compressor terminal blowout) an electrical spark (from the live wire on the terminal blown out) may ignite it. In such an event any R22 also present would decompose into highly toxic fumes greatly increasing the risk of accidental death. As a further caution to tinkerers, commonly available LPG propane (but not R22a or R290) has a sulfer compound "mercaptin" added for leak detection that would have an undesirable effect on the lubrication oil in a sealed system.