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Heater fan electrical issue - UPDATE, Please help

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    Heater fan electrical issue - UPDATE, Please help

    Strange electrical issue.


    Heater fan stopped working completely about a week ago. Did not run on any speed, had previously worked flawlessly. As far as I could tell, the fresh air - recirc function was still working the last time I was driving the car, as I switched between them and could feel a difference. That may matter.


    I ruled out the fuse, and based on my research here concluded that the resistor was not likely to be the issue.



    I removed the firewall cover and blower cover today to reveal a beautiful clean motor and a blue resistor, indicating its been replaced before (definitely the resistor, possibly the motor also.) I turned on the car to test for voltage at the motor, and this is what occurred:


    Initially nothing, then perhaps 0.5 seconds later I hear an electrical switch sound and the recirc button lights up, at which point the fan started blowing. All 4 speeds work. I turned the recirc off, and everything kept running. I heard another sound that was more like a physical click than an electrical switch. I turned the recirc on and off several times and everything kept working, and there were no more electrical of physical clicking sounds.



    The passenger side flapper does not move when recirc is turned on and off, but moves freely by hand. The drivers side flapper still functions as it should. I have no way to know if this was already broken long ago.


    My theory is that the recirc servo got jammed when the passenger side shaft was in the process of breaking. This could have somehow interrupted the whole heater circuit??? Just by removing the cover, it got freed up and is no longer jammed, or finished breaking off completely.


    Is that a sound theory? Is there anything else I should be investigating?
    Last edited by etaFTW; 07-29-2019, 09:03 AM.

    #2
    Well that didn't last. Used the car today and on the final leg of the errand run, the blower wouldn't come on. The only other thing I can think of is that there is a dead spot in motor, and if it happens to stop at that spot, game over. I did spin it when I had opened it up earler, so that may have been what "fixed" it. It looked so I should have taken a closer look at the brand . . . i'll bet its a cheap POS.

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      #3
      UPDATE:

      I opened it back up today for some more investigation:

      Initially I could not reach the negative terminal on the motor, so I tested voltage from the heater fan motor positive terminal to ground:
      Car ignition OFF: 0v
      Car ignition ON, Fan switch OFF: 11.44v
      Car ignition ON, Fan switch 1: 12.06v
      Car ignition ON, Fan switch 2: 12.13v
      Car ignition ON, Fan switch 3: 12.17v
      Car ignition ON, Fan switch 4: 12.22v

      Switch does something, but I was a little surprised by the numbers.

      Once I removed the motor, I tested the directly between the positive and negative wires and with the multimeter set to 12v DC, it gave me readings of -.77 to -.8 volts. I tested the motor for continuity between its terminals and it had continuity.

      The motor is a BEHR unit manufactured in October 2014, and looks clean except some significant oil/grime buildup at the negative terminal. I cleaned it up and put it back in, still doesn't run. I verified that the fuse is still good.

      I am fine with buying a motor ut I haven't convinced myself that is where the problem is. What else should I check?

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        #4
        Another update:


        Applying 12v directly to the motor terminals runs the motor. With the ignition and fan turned on, I get 12 volts when measuring from the positive wire to the chassis (as above), but 0.7 volts when measuring from the positive wire to the negative wire. This has to be a loss of ground in the negative wire. The recirc motor has also stopped working, but was working yesterday when the blower worked, so probably the same ground?



        Where do these ground to?

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          #5
          Bump,

          anyone?

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            #6
            Without studying the wiring diagram I'd say the flaps and recirc should not effect the blower. Have you tested your blower switch ?
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              #7
              Thanks for the reply.

              After getting my hands on a Bentley manual, and studying the wiring diagram (not my forte), I was able to verify that the ground is the problem.

              If I connect the ground terminal on the blower motor to a suitable chassis ground, the blower properly operates at all speeds. The ground goes to G200 above the brake pedal, which has a dozen or so wires to it, and all is clean and intact there. The wire itself must be the issue. I am debating whether to replace the wire along its proper course (massive job), or tap a small hole in the blower motor cover so I can feed the wire out to an alternate ground, which would be WAAAAAY less work. There is a suitable bolt inside the firewall cover toward the drivers side that would work.

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