The abbreviations tell you which atoms are in the molecule. CFC (chlorofluorocarbon): chlorine, fluorine, carbon; examples are R12 and R502. HCFC (hydrochlorofluorocarbon): hydrogen is added to these; the best known is R22. HFC (hydrofluorocarbon): there is no chlorine; R134a, R32, R125 and their blends R404A, R407C and R410A belong to this family. HFO (hydrofluoroolefin): again chlorine-free, but with a double bond between carbons; R1234yf and R1234ze are in this group. All of them are synthetic; they do not occur in nature, they are produced in chemical plants and most contain fluorine.
Each generation arrived to solve the environmental problem of the one before. CFCs thin the ozone layer (ODP around 1); they were phased out by the Montreal Protocol (1987). The ODP of HCFCs is low (0.055 for R22) but not zero; they too were banned in stages. The ODP of HFCs is zero, but their GWPs are measured in thousands: R404A 3,922, R410A 2,088, R134a 1,430. This is why the F-gas regulation and the Kigali Amendment to the Montreal Protocol are phasing down the HFCs.
Because HFOs break down in the atmosphere within days, their GWPs are in single figures (4 for R1234yf). The price is that most of them are mildly flammable (A2L). The refrigerants most used in the field today are the HFO/HFC blends that stand between the two: R449A (GWP 1,397), R448A (1,387) and R513A (631) remain in the non-flammable class A1; blends with a lower GWP such as R454C (148), on the other hand, are A2L. As GWP falls flammability rises; the choice is made according to this balance. That is why there is no single refrigerant that suits every job.
In the field this translates in practice into oil and compatibility. CFCs and HCFCs work with mineral oil, HFCs and HFOs with POE (polyolester) oil; in a retrofit between families the oil is changed. It is hard to work out from the R number which family your refrigerant belongs to; the reliable way is the nameplate and the chart. Outside the synthetic families there are also natural refrigerants: propane (R290), carbon dioxide (R744) and ammonia (R717). Our refrigerant pressure–temperature chart lists the type, GWP and safety class of every refrigerant.