Hey guys new here and I got a 97 Audi A4 and I tried to use the AC recently and it didnt want to work. So I checked the charge and it was fine. The clutch on the compressor doesnt engage. So I talked to the guy that had the car before me and he said it worked fine for him. He then mentioned something about a sensor behind the front bumper that could be causing this problem. What do you guys think, could it be a bad compressor, bad sensor or is there something else that could be wrong with it?

Thanks in advance...