Good call on pulling the car. These electrical system's are very,very complex. You really are not going to be able to "accurately" fix your car without communications with the DME computer on your car. There are so many things that can turn off the a/c command signal and for various reasons. Drivability concern, temp concerns, ect.
You need to find a good independent that has a REAL BMW scanner and can communicate with the DME. A generic scanner will not do it. Otherwise all your doing is guessing and throwing parts at it. My teeth cringe when i hear about mechanics or customers back probing or jumping various sensors on the AC. This can Quickly destroy very expensive modules! This system does not operate like old school cars and uses pulse width and digital data technology and serial communication between the sensors and the various modules. Jumping, test lighting, ect can all damage the circuits and cause a very expensive repair. You will be amazed how simple the actual repair will be on your car when someone with talent and the proper scanner actually diagnosis your car. And thats assuming this last guy did not destroy anything else during his testing.
So make yourself allot of money and find a good BMW specialist in your area, or if you cant find one just bight your teeth and go to the dealer. Even the dealer will be less expensive then your last guy.
Good luck, and if you want to go over any future diagnosis with this problem I will be more then happy to go over it with you!
I think what your saying makes sense. I have one follow up question. The one and only time I took this car to a BMW dealer it cost me $800 with really little to show for it. They performed a lot of diagnostics and they changed the T-stat, T-stat housing, the fan blade and my windshield wiper inserts. One thing that I recently noticed on the over $3,000 list of items on the dealerships "wish list" of repairs that they said my car needed, was the Auxiliary Fan. The BMW dealer told me that it wasn't working. I asked the indenpendent mechanic about this and he said it WAS working. I have yet to see it come on myself. When I activate my A/C which ofcourse isn't blowing cold air, it doesn't seem to come on.
I' m not sure of the functions associated with the auxiliary fan but do you know if this could be a reason for the A/C not working?
It is possible but I dont think so. The Aux fan (condenser fan) will only come on as necessary to lower high side pressures. So even if it was commanded on and did not work the compressor would be turned off, however the next key cycle it would allow AC operation again. I do allot of those fans, they are available after market and are much cheaper then OE. The main complaint of that fan being bad would be "irratic" AC operation. Like waiting at a traffic light my AC starts blowing warm. If you want to go in to the dealer and just pay for a "diagnostic" maybe $100-$150 I would guess. Get all the fault codes and Diagnosis. And then maybe we can go from there.