Unless it has been changed your car is still using r12. R12 uses a screw on still port. If you are trying to add r134 it will not work.
If not converted you will either need to find very expensive r12. Your compressor holds 2.93 lbs. I believe r12 is going for 100 dollars or more a pound. Or convert to r134 which means replacing all of the ac seals, the drier, and putting a shrader valve on the port. The compressor you have will work. Then taking it to a mechanic to put a vac on the system and add the r134. That is if nothing else is wrong, like a leak or a bad line.
If it has been changed there should be a sticker noting that the refrigerant for the system is R134a, and bayonet ports should have been installed. No sticker, no bayonet ports mean no change. If you don't know which port is the low side and you connect a can of refrigerant to the high side, the pressure from the compressor can cause the can to explode. Since it is obvious that you never worked on an AC system before my advice will be to take it in. Better to spend a couple of bucks and be safe then injure yourself or someone else when the can explode.
A forum community dedicated to BMW owners and enthusiasts. Come join the discussion about Bimmerfest events, production numbers, programming, performance, modifications, classifieds, troubleshooting, maintenance, and more! Bringing the BMW community together.