Blower Comes On Automatically

Fellow Enthusiasts,

I've driven my 1991 E34 535i for all of its 14 years and this has never happened, until this morning:

The heater a/c blower was running when I walked into the garage, and making a buzzing noise. It stopped when I opened a door. When the door was shut, the blower came on again in about 20 seconds and ran until the ignition was turned to position 2.

I disconnected the battery for forty-five minutes. The symptom occurred again when I reconnected the battery.

As soon as I turn off the ignition, the blower comes on quietly again for 20 seconds at the equivalent of speed setting # 2. Then in two minutes, the blower starts up again and starts making that buzzing noise. I didn't wait to see how long it would stay on.

Yes, I have an on-board computer with automatic vent timer, but this was turned off. Using the "timer" and "set" buttons would not turn off the blower.

Thanks for any suggestions.

-John S.