[s-cars] r134 in r12 system?

[Ernest Seow]

To retrofit R-12 to R-134a, you will need a new dryer/accumulator, ester 
based oil, and if possible, get the correct R-134 orifice tube if is the 
same fitment (as with the C4 body cars). As for the O-rings. the ester based 
oil is made to be used in either system. Mineral oil differs from PAG, but 
ester works with both. The reason you change the drier is the dessicant 
might be the older XH5 which works in R-12 only.  You want XH-7 or XH-9, 
which most driers/accumulators are filled with now anyway. They should have 
a small label with this code on it. Also if you your vehicle model had a 
R-134a system, then use that charge level. Its usually 75-80% of what the 
R-12 system used to use.
Regards,
Ernest