If you say that some ACC functions work and some don't and banging on the contols gets things to happen then your push-button unit (PBU) is probably in need of a good resoldering. I'm sure a SoCal member can help you get that done. In the meantime, it might help to leave the blower on max and start by using defrost (first button from left) for a couple of minutes then switch to AC (second or third button from left). That got the ACC in my 83 SD going when nothing else would. It could also be worn blower brushes. Banging on the dash can get the brushes to make contact temporarily.

It's hard to say how your AC should perform after the $550 repair. Did he use R12 or R134a refrigerant? If he used R134a, it'll probably provide marginal cooling at best. My SDL was converted to R134a before I got it and it's not fun on 100F days or warmer.

If my sense of time is right, it's been a while since the services were rendered so it's kinda strange that you waited until now to take action on the claim that you did not approve the work before hand.

Good luck.

Sixto
95 S420
87 300SDL