Although R-12 refrigerant is now illegal and no longer available, it is still possible to maintain the older car air con systems typically found on classic cars. Some dealers recommend converting the system to run on R-134a, the modern refrigerant.

We don't.

Be extremely cautious about converting your old R-12 system to R-134a. The R-134a conversion kits sold at car parts shops or online, are called 'Black Death Kits' by some AC engineers as they are usually nothing more than compressed hydrocarbon such as Propane or Butane. The two oils used by each system are not compatible, being quite different types, and frequently, the new R-134a refrigerant will not circulate the R-12 mineral oil and will lead to 'sludging' and seizeure of the compressor. The R-12 mineral oil will also have chlorine contaminants that will destroy the R-134a PAG or POE refrigerant oil.

The only way to reliably convert from R-12 to R-134a is to remove the compressor and flush out all the old oil with the new type of oil;  then separate and flush out all the lines, the evaporator, and condensor with special solvent cleaner, replace all the 'O' ring seals with R-134a compatible seals, then flush with OFN, then replace the old Receiver-Dryer or Accumulator with a new one; next, vacuum for at least 40 minutes and finally re-charge with 70-80%, (by weight) of the original R-12 weight, with R-134a and add the correct amount and grade of PAG oil. Done correctly, this is an effective if expensive conversion, however, there is another way.

It is much more cost effective to keep the old R-12 system and simply recharge as normal using RS-24 refrigerant or similar 'drop in' replacement, which will also have the added benefit of keeping the car as near original as possible. Whilst this will require a special Esther oil and a separate set of equipment, most specialists will have this AND the cost is only a little more than for a modern, R-134a based system.