AC clutch is triggered by the DME. Does the aux fan in front of the radiator come on? Do you have a scanner for scanning for faults? I had a bad aux fan and the compressor wouldn't engaged. Scanned the X with my scanners (carsoft 6.5 and BMW Scanner 1.4) and they both indicated a bad fan. Replaced the fan and the AC is working again, just in time for summer.
Good Luck with your AC problem.