2002 E39 525i SE Re-occuring FSU Fault: Need expert advise

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  1. 2002 E39 525i SE Re-occuring FSU Fault: Need expert advise 
    #1
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    GavB's Car Details
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    I seem to have an ongoing saga with my climate control heater, i'm now out of ideas - need some advise regarding possible electrical faults.

    History
    Had the typical erratic heater blower motor behaviour about 12 months ago, removed what looked like the original FSU (Hedgehog) and replaced with a cheap Ebay jobby. Fault fixed.

    6 months later Heater Blower wont work, no erratic behavour like before so think maybe the actual blower motor has failed. So removed the FSU and bypassed it, the blower motor did work when supplied 12V. I decided it must be the cheap FSU that failed so bought a OEM version and installed it. That solved the problem.

    Full history here 2002 E39 525i Heater Blower Diagnosis?

    Roll on just two months and the heater stops working again. Very suspicious that the OEM version is unlikley to be faulty, I wonder if something may be causing it to fail, some kind of electrical fault? So I removed the FSU and used a multimeter to check out the voltages.

    These are the results of tests at the connector block to the FSU.

    With engine off / on:
    PD between power wire from fuse and earth wire: 11.9V / 13.9V
    PD between power wire from fuse and chassis/ground: 11.9V / 13.9V

    Resistance to earth down earth wire: 0.1 ohms

    With engine off / on:
    Power drawn by blower motor when FSU bypassed: 15.5A / 17.5A

    PD between control Signal and chassis/ground:
    0.1V off
    2V one bar on display
    2.3V
    2.5V
    2.9V
    3.25V five bars
    3.55V
    3.9V
    4.1V
    4.4V
    4.7V ten bars
    5V
    5.35V
    5.75V
    6V
    6.3V
    7.6V Full On

    With the engine on control voltages were approx 0.3V more.

    After doing all this I reconnected the FSU, and very suprisingly everything worked Okay again, I thought maybe a loose connection, and was happy, but less then a week later, stopped working again.

    Have removed the FSU again tonight and checked the motor works again by bypassing. Reconnected the FSU, does not work.

    I also noted that with the FSU connected, as soon as the heater controller is turned on the FSU gets very hot, hand burningly hot!

    SO:

    I can return the OEM FSU for a replacement under warantey - but what is the point if this is not the root cause and something else is causing the FSU to fail. However looking at the voltages I recorded I can't see what could be causing it to fail. I am only an amateur dabbling - any more knowlegable folk got more ideas???

    Many thanks.

    Gavin
    Last edited by GavB; 25-10-2010 at 19:50. Reason: link added
     
     

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  3.  
    #2
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    TheEnd's Car Details
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    I think you have a fair case to, although it does seem to be an intermittent fault.
    The car side voltages all seem fine (although this is based on what i would expect, not what i have seen written/measured)

    The one thing that i would be interested in looking at would be the power draw when bridged, incase the fan in overloaded, but again, your 15 / 17A is what i would expect.
    If it was drawing too much from motor windings, I'd expect the fuse to blow first.
    The heater blower is listed as having a 40A fuse, so I'd expect far higher current readings to be cooking the Hedgehog.
    They will get hot anyway as a matter of course, hence the very spikey nature of them.

    I've had a look in the WDS http://www.bmw-planet.com/diagrams/r...9new/index.htm
    But only wiring diagrams, and an overview of the heater control panel operation, no testing data
    Under components> K- Relays > K4 Heater Blower Relay, there is a relay, but I'm not sure if the FSU system takes precedent.

    There doesn't appear to be any info under components>signals>M>Motors>MOT+ / MOT- either.
     
     

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    GavB (27-10-2010)

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    colin.ab's Car Details
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    If the FSU is gettign red hot (ouch thats my hand burning!),then it is supplying power to the fan. It is possible that the bearings on the fan are failing. Low power drive from the FSU is not enough to make the fan turn. Shorting out the FSU applies full power to the motor, which gets it moving and unseizies the fan.

    Look like you'll be needing to remove the whole dash to get to the fan!

    You can touch the fan by removing the ducting from the engine bay and sticking your hand in the hole (bit like vets in All Creature Great and small). You may be able to feel if the bearings are stiff. Has it been making any odd noisies lately?
     
     

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    GavB (27-10-2010)

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    #4
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    Thank you both for the detailed replies.

    Colin, I have some recollection that occasionally the fan would squeak a little when it first came on. However I have tried turning by hand (I know what you mean) and it turned quite freely.

    It is an interesting theory that the motor needs a more initail voltage than the control signal is asking for to get it moving beyond an increased bearing resistance, and perhaps a prolonged duration of this my kill the FSU without me knowing that the fan has not come on when called for. As the TheEnd says though the amps look normal so its not that seized.

    I was really hoping that I wouldn't need to change the Blower Motor.

    Maybe the next step is to get a variable resistor and try to manually mimic the FSU and see if the fan will always come on when on a low setting - Could actually be quite a good temporary solution for winter if I can mount it somewhere convieniant!!

    Anyone guess what the range of the resistor would need to be?

    Thanks.
     
     

  9. 2002 525i Sport fan blower 
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    am new to site and trying to fathom what's going on with my fan blower and enjoying reading your exchanges. The fan seems to have stopped working totally and my initial guess is the fuse has gone but cannot seem to locate it. Any ideas?
     
     

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    Quote Originally Posted by pjal4 View Post
    am new to site and trying to fathom what's going on with my fan blower and enjoying reading your exchanges. The fan seems to have stopped working totally and my initial guess is the fuse has gone but cannot seem to locate it. Any ideas?
    In the fusebox, near the passenger side turret !
     
     

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    That's funny Fuse 76 on mine is under the glovebox.
     
     

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