I have read that when converting an original a/c from R-12 To 134A you only use 80% of the original amount of R-12. Have not seen any thing about the amount of compressor oil to use. The 68 Camaro system used 11 oz. of oil originally. Do you also cut the amount of oil to 80 % also?
Thanks

Under pressure, the 134 is more in VOLUME, so reduce it normally 80%. do not use less oil.
Have you flushed the system? Not good to mix r-12 and 134....

Paul,
If your converting over to 134a I recommend that you get the conversion kit. In it you'll have the correct o-rings for all the fittings and enough oil to do the trick. You'll also need to change out the accumulator (drier) as well. Reason being is that it still has oil in it and you dont want to mix the oils. Isolate the evaporator and condensor and flush those out. Dont flush the expansion valve. Put everything back together and pull a good vacuum on the system, leak check and then charge the system.
Good luck.

there is an system flush for this also to run thru the condenser, basically neutralizes the old remanining contents. If you cant blow air thru this condenser well, its probably corroded internally, get a new one. It will keep tempatures down on compressor. For final flush pressure, try to use nitrogen if possible. You want to elimanite as much moisture as possible.
When adding entire amount of oil. put about half in compressor suction and rotate compresser internals, put remaining in to new accumulator.

And don't forget. The old oil has gotta go. It's not compatible with 134A. Clean, clean, cle
Wanna borrow my nitrogen tank? Vacuum pump? Clean!

Thanks to each of you that replied ! I will follow your advice to the letter.
Paul

when my shop converted me to R134 they flushed the system and then added some Ester Synthetic oil to the system from a small bottle they have in stock. Talk to a few good shops that do a/c work and get the right info. :)