For the last month or so, the blower motor in my 87 300D has worked only intermittently. It would always run with the key in the on position, but once you twisted CW to start the car it would cut out and usually would only come back on after stopping and starting the car a few times. Last weekend I installed new brushes hoping that would solve the problem - it didn't.
That kind of bummed me out, as any other fix would probably entail money that I'd rather spend elsewhere on the car, so I got to compalining about it to the GF. Then she tells me that it always works perfectly when she drives. Well, WTF? So I grab her key and go for a spin. Blower blows nice cold air. The next day, I take her key again and the same thing.
Hmmm.... the only thing different here is that I'm using her nice new key that I had cut at the dealer, instead of the ratty 17 year old key that came with the car - How can that make a difference? So, I start the car with my key again, and no blower. Then I turn the key just a CH CCW and the blower starts. It appears that when my key is used, the ignition doesn't return fully from the start position to the run position on its own. After several days for testing now, I can verify that the key/ignition issue is the cause of the blower motor problem. And, as a bonus, the cruise control works again too!
