My sypmtoms matched your pretty well. You definitely have the FSR problem.

For 3 days the front blower didn't work at all.
For 2 days it worked fine, with total control.
I parked it for 7 days, then found I had no control at all with erratic fan speeds.
Throughout the ordeal the rear blower worked fine, with nice cold air.
I replaced the FSR and all is well.

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2002 X5 3.0i