There are two refrigerants authorized for use in automobiles in the USA, R-12 and R-134a. They both work equally well. The A/C components, that is the Compressor, condenser, evaporator, filter dryer (acumulator /dryer in Fords), expansion valve or in Fords an oriface tube, and the high and low pressure lines and manifolds, are not specific to either of the refrigerants.
The two differences that must be considered are the seals ("O" rings), and the oil. Some properties of R-134a necessitate seals made of a different material than those used for R-12. Otherwise the "system" works exactly the same with either refrigerant. But, the refrigerants cannot be mixed and neither can the oils. You either use one or the other, but the correct seals and the correct oil must be used for the refrigerant you use.
If you want to save money then convert your R-12 to R-134a. Otherwise the R-12 refrigerant could cost you as much as every thing you need to do to convert to R-134a. R-12 is near $200 per pound in some places and it will get more expensive as it becomes rarer. It is no longer legally made in the US and cannot be legally imported. There are a few purported substitutes being sold, but beware they are EXTREMELY dangerous to use. They are explosive. rangerj
