Is it necessary to add compressor oil when recharging A/C?
The rule of thumb is if you do a repair on an A/C system; what ever part you take out and drain you put in the same amount of oil that came out back into the system.
Unless you have a big leak you usually do not have to add oil.
Too much oil can cause complications with cooling so the correct amount should always be in the system.
If the car or truck is old and not cooling properly and there is no leak then just add the recharge amount and stay cool.