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A/C fan surging then quit

Discussion in 'E46 (1999-2006)' started by wardlowk, May 27, 2010.

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    wardlowk

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    For the past year my 2003 325i A/C fan has been surging and this morning it finally quit. It would have to do this on the hottest, most humid day so far this year. This must be a common occurance because my wife's 2001 325i started doing the same thing right before we sold it. Any advice as to what it may be and if there are any DIY links on how to fix it. Thanks!
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    Zeichen311

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    You're right, it's a common failure on a number of early-2000's models, especially the E46 (1999-2005 3 Series). Search for "final stage resistor" or "final stage unit" to locate more information and instructions. This unit was prone to failure due to an inadequate heat sink and has been superseded by a new part.

    It's a simple repair but a bit of a PITA because the FSU is buried in a most inconvenient location: under the center of the dash, inside the HVAC ductwork. It is accessed from the passenger footwell but depending on body style, gaining access may require a lot of seemingly unrelated disassembly. This is one of those paradoxical jobs where the more you take apart, the easier it is. You will be working in a very cramped area. The more working room you create for yourself, the better.

    If you plan to keep this and do more DIY repairs, invest in a Bentley service manual for the E46 right now. You will break even on this job alone (the part and manual are about $100 each). The instructions for this job, and in general, are better than any amateur write-ups you will find on the web.
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    jrj127

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    wardlowk

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    Maybe this is my lucky day. I was heading out at lunch today and the fan worked perfectly. I know it is just a matter of time before it goes out again but maybe I can avoid having to tear into the dash a little longer.

    As far as Pelican parts, I have ordered from them several times and have been very pleased with their prices and available parts.

    Thanks for your replies.
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    Zeichen311

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    You can usually ignore a failing FSU for as long as you can stand it. The car doesn't seem to care, with one exception: Be prepared for the possibility of waking up to a dead battery one morning.

    The HVAC system runs self-diagnostic and self-maintenance cycles after you shut the car off. These can sometimes get "stuck" when the FSU is on its last legs, running the blower at medium to full speed for hours. Overnight, that's enough to drain the battery too low to start the car.
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    wardlowk

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    Thanks for the warning. I have learned over the years to keep jumper cables in the car.
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    bcweir

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    It's helpful to have a second car available too for those jumper cables

    The jumper cables by themselves won't save your bacon. LOL. Good luck with this repair and let us know how it goes.

    SounderBMW guest

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    This just started happening in my 2001 325. Thank you for all of the info. Going to give it a go on the DIY.

    unboringuy guest

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    Yesterday when I had a brake job done on my 2001 330xi, the A/C wouldn't come on. A few minutes later it came on and seemed to work fine. This morning the same thing happened, and a few minutes later it came on with the fan running at full speed regardless of the setting.
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    mooseheadm5

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    Yup, same issue.

    unboringuy guest

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    Moosehead, this occurred for the first time when I picked up my car after a brake job. Is this just dumb coincidence? The shop says there is nothing they could have done to have caused this problem with the final stage resistor.
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    • Technical Service Advisor

    mooseheadm5

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    Definitely a dumb coincidence. The part is a very common failure item and there is no way to make it go bad by doing anything other than using it, which you have been doing ever since you owned the car. The part is not ridiculously expensive and has been updated in design for (hopefully) longer life.

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