I purchased a high mileage 190d with a non-functioning A/C. Took it to an independent shop to see if they could troubleshoot the problem. Ended up putting in a GM pressure switch with a rocker switch to activate the A/C instead of the climate control system. Now when the A/C is going I can actually hear a half second sucking sound through the middle vents. This occurs about every 4-5 seconds and also causes hesitation in the engine. Any ideas? Also the transmission acts like it is slipping, (revs to 4000 rpm if I don't release the accelerator), going into 2nd and 3rd gear when I first start and run the car. This is a new transmission about 30K ago.