Aux fan & AC issues

[Mgross]

Hello folks -
I recently purchased a used 2008 E70, 3.0si, 90k miles. My wife was driving it one day and the water pump failed. The aux fan spooled up - fortunately she was able to limp it 5 miles to home. I replaced the water pump (actually not that hard of a job) and changed/checked the oil to make sure we hadn't damaged anything. Oil looked good, car runs fine.
Anyways, ever since replacing the water pump (yes, its OEM) the air conditioner hasn't worked - as in the clutch doesn't engage the compressor - I can see that if I peek through the front grill. I have also never heard the aux fan turn on once since the water pump replacement, even if I turn on the air con to max. I believe this is supposed to automatically engage the aux fan regardless of anything?
The aux fan is getting power supply (volt meter check on the red/black leads) and the little wire (signal wire) shows ~3/4 volts (can't remember exactly what it was. So while I was tinkering with this, I grabbed the fan and tried spinning it by hand. it was hard to turn, and almost felt like it was indexing on something - like if you try to turn a stepper motor by hand. Anyways, after I did that the fan turned on full power for about a minute and then shut off again - but still the compressor clutch did not engage.


So I am at a loss here. Do I risk a $500 aux fan replacement? It sure seems that way, but I don't want to be wrong...

Thanks