The refrigerant used for many years in automotive air-conditioning systems is a substance known as Dichlorodifluoromethane - commonly referred to as Freon or R-12. It is one of a group of gases called CFC's.
R-12 has the following properties. It is non-flammable, non-toxic, is stable at all temperatures, does not react with aluminum, steel or copper, and it is soluble in mineral oils.
It also has a low boiling point and vaporizes at minus 30°C.
However it was found to be harmful to the environment and a number of alternative refrigerants were considered to replace R-12. The most practical of these being a liquid known as R-134-A.
R-134-A is a refrigerant suitable for use in automotive air-conditioning systems. It is an HFC or Hydrofluorocarbon. It does not contain the ozone depleting Chlorine atom.
R-134-A has a boiling point of minus 26.2°C. All its other refrigerant characteristics are similar to R-12. The only difference being that its operating pressures and temperatures in the evaporator and condenser are slightly higher than for R-12.
There are important differences in their chemical properties. Unlike R-12, R-134-A is not soluble in mineral oils, so new compressor lubricating oils have been developed.
To prevent the wrong lubricant or refrigerant being installed during servicing the service ports on air-conditioning systems have been changed so that the service equipment for an R-12 system cannot be connected to an R-134-A system.