Only reason to add oil is if components are replaced.

First step is to get the system pressurized with a dry gas and verify no leaks.
Next, of course, fix any leaks found, and reverify.

If you are replacing the compressor, it will need 2oz of oil... If you are replacing it, you will also need to replace the receiver dryer and it needs 2 oz oil. Any hoses needing replacement, need a tiny amount of oil. Condenser and or evaporator coils also would need some oil if they are being replaced, or if you are flushing them out with cleaners.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!