Air Distribution motor - question

[scott 4991]

So, quoting the Bentley manual, "The distribution of air is controlled by a series of flaps that are actuated by stepper motors". When replacing my microfilter today, I find the stepper motor, passenger side, laying out of the 'socket' it sat in, the plastic retainer had broken. Ha, this explains a heating issue!.. anyway, I wanted to see if the stepper motor worked so I ran the car, it worked fine (I think) but went to one location which I will call the 9-3 location, indicating the servo motor has the arm turned to the 9 o’clock and 3 o’clock position. The valve inside where the stepper motor is to go only moves from 10 o’clock to 2 o’clock, so somehow I have to reposition the stepper motor, then secure it back into the holder somehow, then BE SURE the stepper motor does not try to turn back to the 9-3 position or it will break again - this is perhaps what caused it to break the 1st time. There is a chance the stepper motor control is not working and the motor goes to one extreme position - I will check this tomorrow when the car gets warm and I control the heater valves from the controls.

Any suggestions?

Thanks

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[scott 4991]

Found out that the left temp dial (drivers side) controlled this stepper motor. The motor worked fine, but as I held the motor in place and turned the drivers side heater dial, I could feel the motor straining to turn the valve past the valve limits, which controlled the air flow. Not sure how this happened??? Anyway, I took the stepper motor apart (picture) and manually turned the brass looking guide so it aligned properly with the valve it mates up to. Now it works fine, the valve opens and closes as it should. Now to get the stepper motor fixed in place as the plastic has broken.. but thinking come sort of "C" clip or tie-trap may do the trick.

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[scott 4991]

Here is the final picture, works great. I used a little 5 min epoxy and a little RTV for any future movement.

sc

[632 Regal]

impressive! Never saw this problem or a fix, good job.

[scott 4991]

Thanks, I too am puzzled as to the cause, and I think perhaps, it's been like this for a long time - perhaps forever! I did not see any of the gear teeth broken, which is what I would expect to see - they are plastic gear teeth in the black housing, and a metal gear on the motor. If it slipped, it should have broken the plastic teeth. It did not. The only thing I can think of is that at some point in the cars life, something fell through the vent and blocked the valve from moving all the way. The motor then would have kept turning - the gear ratio is very large / powerful. Then if the motor went back the other way, freeing the item that fell, perhaps this was the cause? Who knows.

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[scott 4991]

After driving the car now, the heater now pushes air throught the front vents and all works great. I wonder how long this servo motor has been broken? Boy do I love 535's!!

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[Kalevera]

Curious -- what's the production month of the car, and is it a US car? I've never seen a non-M US spec MY 1990 E34 with a microfilter.

[scott 4991]

When I got into the disassembly of the car to replace the microfilter, I found there was no microfilter - I returned the one I bought to BMA for a refund. All the books I have indicated there was a microfilter - not in my 535i.

sc