Re: AC High Pressure service port
Ummh, not to be rude, but you do not require any sort of license to handle R-134a. Wisconsin does require licensing to even purchase any refrigerant. Only the chlorinated ones, such as R-12 and R-22 require an EPA license.
That said, if the system is opened, it should be evacuated before re-charge, and you likely cannot do that. There is a relief valve on the high side of the compressor that is spring-loaded, and if that valve let the refrigerant out, you have a deeper problem. If it is the access port, it should have had a red(?) plastic cap to protect it from dirt, and then a schrader valve under that. The schrader is just like the valve in a tire stem. They should not leak under normal conditions.
The capacity is stated in oz, and that is the refrigerant only. The oil capacity is factory determined, and not usually stated on the underhood tag. If significant oil is lost, for whatever reason, such as changing the compressor or the accumulator, every remaining component in the system, including compressor, should be flushed as clean as possible and a full oil replacement made. Other than doing that, you are just guessing. AND so would any mechanic who added lube willy-nilly. You likely can get away with adding one oz if you think your loss is minimal, but not much more than that.