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Thread: Stepper motor for HVAC system question

  1. #1
    Join Date
    Mar 2004
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    Default Stepper motor for HVAC system question

    Is the stepper motor located at #3 in this picture supposed to turn 360 degrees? There is NO #6 motor on my E34 535i. It appears mine DOES turn 360 degrees has therefore has broken the mount, cracked the heater box and the actuator rod has popped off (due to no clearance for the revolution). I've gone thru the documentation and fixes for the mount, but I didn't see a mention of whether or not the motor is supposed to turn 360 degrees.

    I've been watching the motor movements (since I had to change out my heater core) and it does a couple of things:

    (1) rotates 120 degress when I turn the ignition on
    (2) rotates another 120 degrees when I turn the ignition off and then back on again
    (3) this cycle continues no matter how many times the iginiton is turned on
    (4) with the car on and the defrost vent opened, the motor turns 120 degrees
    (5) with the car on and the defrost vent closed, the motor turns BACK 120degrees, back to the origin in #4 (ie, never making a revolution).

    So my question is, is this motor supposed to turn 360 degrees?

    Thanks!
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    Last edited by bmwpower; 01-06-2008 at 12:32 AM.

  2. #2
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    Dec 2003
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    I have my car in pieces just like that at the moment so I will check next time I'm there. I will have to re-assemble some of it to be able to turn the igntion on. Hopefully I will be able to do that tomorrow afternoon if everything goes to plan with the evaporator replacement.

    From memory that stepper controls the temp of the air coming out of the face vents and is controlled by the wheel between the two centre vents. When the car is off the vents are opened, and when the car is on they are closed if you have the wheel set to cold, otherwise they are open. There is also some control logic that help to control the temp correctly.

    I'm not sure about how far it rotates, so will have to look at that.

  3. #3
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    Quote Originally Posted by myles
    I have my car in pieces just like that at the moment so I will check next time I'm there. I will have to re-assemble some of it to be able to turn the igntion on. Hopefully I will be able to do that tomorrow afternoon if everything goes to plan with the evaporator replacement.

    From memory that stepper controls the temp of the air coming out of the face vents and is controlled by the wheel between the two centre vents. When the car is off the vents are opened, and when the car is on they are closed if you have the wheel set to cold, otherwise they are open. There is also some control logic that help to control the temp correctly.

    I'm not sure about how far it rotates, so will have to look at that.
    Thanks, that would be great as I really don't want to put it back together without it working correctly.

  4. #4
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    The output shaft on mine only rotates 90 degrees. I didn't remove the stepper motor from the mounting bracket though. When I turn the ignition on the vent closes and opens when the ignition is off.

  5. #5
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    Location
    NJ
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    Default

    Quote Originally Posted by myles
    The output shaft on mine only rotates 90 degrees. I didn't remove the stepper motor from the mounting bracket though. When I turn the ignition on the vent closes and opens when the ignition is off.
    Thanks! That's what I was afraid of. I'm assuming the motor will continue to turn like mine if you remove it. It's the mount that stops the arm from turning around all the way....and mine is broken.

    Somehow I'm going to have to fab up something to keep the arm from turning all the way around....and hopefully the motor will stop.

    If you still have the thing apart, can you check and see what the motor does when it hits the stop? I'm assuming it torques up a couple of times and then stops moving. I just want to make sure the motor's not malfunctioning and NOT stopping when it hits something.
    Last edited by bmwpower; 01-05-2008 at 05:29 PM.

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