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HVAC fan runs all the time

Discussion in 'E39 (1997-2003)' started by myronm, Oct 15, 2010.

    • Member

    myronm

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    I gave my son an '03 525i a few years ago and it has developed a new issue lately. My son had complained that the battery would be drained flat overnight. He would disconnect the battery so he was able to start it the next day.

    I got in the car today and noticed that the interior fan blows even when the key is not in the ignition. I have searched the usual web sources but did not find anything that addresses this type of failure. Most of the issues concern the "Final Stage Resistor" dealing with the fan speed control.

    Anyone experience anything similar? Suggestions?

    Thanks,

    Myron M.
    Ft Worth, TX.
    • Member

    bcweir

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    Most likely the resistor on your fan is shot.

    What you described is a common issue with these cars. 9 times out of 10, replacing the final state resistor resolves the issue.

    Other possible causes are your IHKA (HVAC control) or your "sword" (fan control relay) has gone bad.

    I'm going to go with the fan resistor as the most likely suspect.

    If I had the last 7 digits of your car's VIN I could assist you in finding a replacement.
    • Member

    myronm

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    Thank you for your help.

    I searched realoem.com and bavauto.com & just ordered a final stage resistor.
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    • Technical Service Advisor

    mooseheadm5

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    E39s don't have a sword, they have the final stage resistor (which is actually a transistorized controller.) This is definitely your issue. The new design is leagues better than the old design. It is pretty easy to replace, too.
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    bcweir

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    Thank you Moosehead!

    Great information
    • Member

    myronm

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    If I recall correctly, the E34 used a sword to control the fan speed. I have found instructions for the installation of the final stage resistor for my E39. Looks like it's a project for a Saturday afternoon before the Warsteiners kick in.

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