the low side fitting is on the back of the AC compressor. the high side fitting is right next to the passanger headlight behind the grille

Great advice, chargers, except it is WRONG. Any checking on your part would show that freon charging equipment will not fit that port since it is not designed for that purpose and a work-around to make a fitting adapt could lead to damage to the compressor.

The system is serviced through the high pressure port on the compressor. There are fitting differences between R12 and R134a systems, so if you have an early model S4 you need to recognize the difference. There are some
who have used adapters to top off the system with the 12 oz cans, but you need to search for that information.

don't encourage him...lol, seriously needs to pull his (her?) head out of his ass and stop dredging up old posts........although, I guess in the big picture I'm a couple days late myself. In my defense I don't come by this forum much anymore. Let's not direct this one anywhere else..mmmkay? lol