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  1. #1
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    Final Stage Unit (FSU) question

    I just replaced my final stage unit on my 528i, which was nothing short of 15 minutes of a neck straining experience. Anyhow, everything appears to be a success, however, rather than my blower blowing only at a low speed, it's now constantly blowing at a high speed; adjusting the speed has no effect, and when my car is off, I can still hear the fan running as if I had turned on the 'rest' button, which I haven't.

    My question is this: Is this common? Will it eventually 're-calibrate itself and return to normal? I have the right resistor (FSU) part even though it's an aftermarket and not an BMW OEM part. I made all the right connections after I installed it. Is it this new resistor that's the problem?

    Your thoughts?


  2. #2
    Ed CT
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    Sounds like what a bad FSU does...

    Some of those aftermarket components are just not good.
    Was the old FSU running only at a low speed? If your neck can stand another :15 minutes, try putting the old one back in to see what happens. Or, a hard re-boot (discon the battery terminals, touch them together, turn on ignition for 15 seconds then off, reconnect battery)

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    Re: Final Stage Unit (FSU) question

    My speculation:

    Many people end up changing the FSU because they have a battery drain and are concerned the FSU is not turning off after the car is shut down. I don't know if that's why you changed it in the first place, but you now obviously have the problem a new FSU is intended to solve. All I can suspect is a faulty FSU right out of the box; I'd at least swap in another one to see if the problem continues, in which case it's likely the circuit.

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    Re: Sounds like what a bad FSU does...

    Thanks Ed for your response. Yes, the old FSU was only running at a low speed. At the moment, I don't mind the blower running at a high speed considering it's winter time and it's better for the blower to be running high than running low. My only concern is if this blower continues to run when my car is off, it will drain my battery. But I will give your suggestion a try and see what happens. Thanks!

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    Your new one is bad, there isn't any calibration (

    The FSU has 5 pins in it, 2 are for power from the battery, 2 are power to the blower motor, and the last pin is the control signal from the HVAC panel that controls how much current passes thru the FSU to the blower motor. When the car is turned off the blower should stop. There has been a number of posts recently about aftermarket FSU's not working properly.
    There is the possibility that your HVAC panel is bad if the blower motor is operating exactly the same with this new FSU as it did with the old FSU.

  6. #6
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    Re: Final Stage Unit (FSU) question

    ZeroDfx:

    My problem was not that at first (original FSU got old and blower was running only at low), but what you just stated, that seems to be my problem now,- my new FSU doesn't seem to be turning off. Lesson to be learned: when an e-bay seller is selling two of the same parts, but one is significantly cheaper (but also new), don't buy the cheaper one. He obviously knows something we don't.

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    Re: Your new one is bad, there isn't any calibration (

    Thanks Jim, but I'm not sure if it's the HVAC panel because with my old FSU, my blower did turn off when my motor was off; the old FSU was only allowing the blower to run only at a low speed. But this new FSU is constantly running at a high speed and is not shutting off when my motor is off.

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    I only mentioned that as a possibility, but with (

    what you have said it's definately a bad FSU.

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    I long for the days of three speed fans and a

    dial from cold to hot to change temperature. All of these electronics simply make for more things to go wrong, and they do go wrong frequently.

    jet black 2000 528iA
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