Me again...computer problem now?...

Hello,
I just bought a 2000 540iT w/100K miles; time/distance did not allow for a correct pre-purchase inspection. (shame...)
Self-leveling suspension error message is on, AC compressor will not
come on. All else 5 X 5, runs like scalded cat.
My mechanic (very competent) checked refrigerant level (OK); compressor will function when energized directly. All fuses, connectors OK. His diagnosis; remove/replace main(?) computer.
Any pro/con thoughts? Good source for replacement device?
Thanks in advance!
Cheers,
f.
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1-Did you checked the a/c relay (behind the fuse box, you have to remove glove box compt.). 2- Is your outside temperature in the cluster is working and indicating over 1 degree C ? If not, by default, after a certain number of run of the a/c the IHKA "knows" that the temp. sensor is not working properly and lock the a/c to off position. A shorted or disconnected sensor will show -40C and after installing a new one or reconnecting or repairing the wiring it will take about half an hour to display the right temp. 3- If your electric supplementary fan is in fault your a/c will not work. 4-A pretty much frequent problem is the pressure switch on the receiver/dryer being stock on the "too high" or "to low" side and disable the compressor. By memory those are the few potentialy reasons why your a/c is u/s. But If your very competent mecanic don't have the proper equipment to read and clear the fault(s) in the car's memory system, you will lost a bunch of time and money and your system(s) will never work. Basically your 2 problems here requires quite a bit of research and the first thing to do is to "read" the faults, so find a good specialise BMW garage or go to the dealer, they will be more expensive on the hourly rate but they must fix your problems fairly quickly.(or at least let you know) Last hint before going to the garage. If your are pretty shure everything is find with parts and wiring, try a complete reset of the car by disconnecting BOTH cable (positif and negatif side) from the battery post and make them touch togheter for 10-15 seconds. This will discharge all the condensers/capacitors in all the control units/computer in the car and reset almost everything to the original setup. If you're lucky and your problems were only glitches in computers everything maybe back on track.
Good Luck

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