R-12 and R-22 are totally different products. R-22 was used in most large capacity air conditioning units...10, 20 30 ton and up chiller units. R-12 was the old stand by for most small refrigeration units and the automotive industry till the Feds outlawed it's production and importation into the US in '92 or '93. R-12 is the stuff THEY were most worried about. It is an HCFC (hydrochloroflourocarbon), chlorine being the component which THEY claim will damage the ozone. That is why it costs over 20.00 for a 12 oz can. The only legal source for the stuff is what's recovered from the field, and recycled back into "virgin state refrigerant". What do you think they do with all that R-12 they charge you exuberant prices to recover.

They let R-22 stay around a few more years because it didn't have the chlorine. These substances, of which there are hundreds, are used as refrigerants because they have the proper "pressure/temperature relationship". In other words, when placed in a sealed unit or container they have a precise and predictable pressure, dependant upon their temperature, and vice/versa.

R-12 in a sealed bottle at a temperature of 81 degrees will have a pressure of about 85 PSI. R-22 in a sealed container at 81 degrees will be 145 PSI. Therefore they cannot be interchanged. They should never be mixed or a completely different substance would be created which would have a very different "pressure/temperature relationship"

R-134A is the supposedly ozone safe product to replace both. But realize this: since R-12 and R-134A have a VERY similar "pressure/temperature relationship", R-134A can be a drop in replacement for R-12. BUT, before R-134A can replace R-22 the entire system pressure has to be redesigned (different compressor.)

PS. for the environmentally friendly, the US Coast Guard and US Navy have just about completely retrofitted every ship's refrigeration and air conditioning systems with R-134A. It's a lot easier on the technician cause now we only have to maintain service equipment for one type of refrigerant.....recovery machine, gauge manifold, etc, etc

Regards,
Earl F. Allen, Jr. MKC, USCG