there is some R-12 HVAC system still around but they are no problem to
deal with for you replace the freon and oil with ester Oil and 134-A like
in cars. now you should recover all the R-12 and put all fresh R-134-a in
it with new Ester oil.


you can't do that in cars, often the o-rings in the hose connections and in
the compressor in an R-12 system will not tolerate ester oil or other 134a
oils such as PAG, beside how do you plan to remove all of the old mineral
oil with a complete system flush with solvent?

not to mention the fact that unless you replace the condensor with a
high-efficiency model, the cooling will be much less with 134a than it was
with R-12, because 134a is a much less efficient refrigerant

this is why the fins in the condenser in newer cars are much more tiny than
they were before about 1994 or so


cheers!

cowboy
auto A/C oracle