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Intermittent heater blower fault - 2009 A4 2.0TDI 143

Number8 Aug 10, 2018

  1. Number8

    Number8 New Member

    Hi there,

    Could anyone offer some advice? I have an intermittent heater blower fault, and haven't come across a similar problem in other threads.

    Car – 2009 Audi A4 B8 Avant 2.0 TDI 143, 130,000 miles

    Problem – Intermittent heater blower/air-con

    Scenario – First thing in the morning on daily commute, the blower comes on as soon as the car is started (normally goes to auto). I can then switch the air-con on and adjust the blower speed up and down and air direction as required. The air-con is fine – icy cold when it comes on. However, if I go to use the car during the day, or when I drive the car home in the evening, the blower refuses to function in any setting.

    I have tried all of the following combinations while driving to get it to work without success:

    - air-con on/off
    - leaving all settings in auto
    - changing blower speed
    - recirculation
    - nothing at all (off), then on again repeatedly
    - parking the car in shade
    - leaving windows open
    - even stopping the car halfway from home, locking it and coming back to it!

    None of these make a difference. Sometimes the blower will suddenly come on when nearly home (a distance of about 30 miles from the office), sometimes not at all. Occasionally if I go out later on in the evening, for example, to move the car off the drive later at night, the blower will come on again at full blast.

    As you can tell, it’s quite annoying, and seems to have a mind of its own, although does seem to follow a distinct pattern. I’d normally ignore it and open the window, but having a new baby, sometimes I need to cool the car down more quickly, so I could do with rectifying this fault. I have tried the following:

    - disconnecting and reconnecting the battery
    - checking for fault codes with OBD-II reader - none detected (I do not have access to VAG-COM)
    - clearing all vents inside and out, cleaning leaves etc. from the engine bay
    - taking the blower motor out from behind the glovebox (now I have the infernal airbag warning light on!) – spins quite freely
    - parking in shade/leaving windows open
    - shouting at the car!

    This feels like the classic intermittent fault that I’ll never fix – unless I chuck money at it, but at which parts? Does anyone have any suggestions?

    (Side note - I am about to take the car to an independent garage to have the cambelt and water pump changed as I'm not sure when/if it was previously done).
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  3. Kennyken

    Kennyken New Member

    Could be the blower resistor, that's what it's been on previous cars I've owned with this problem. I currently have this issue on my 09 a4 also

    JONATHAN GRAY New Member

    Having the exact same problem on my a4 at the minute, really frustrating. Did you find out what was your problem?
  5. Number8

    Number8 New Member

    Hi Jonathan,

    Not exactly - but funnily enough, after getting nowhere and five months since posting on here, yesterday I decided to do something about it as my occasional commute has been getting seriously cold!

    I didn’t get any answers from Google, and worked out it wasn’t the resistor as there was no air at all from any controls. There was residual heat, i.e. if all vents were open, then I could get air to come into the car which would feel warm-ish.

    Anyway, I thought it must be the blower. So I rigged up a car battery on the bench and removed the blower motor unit from under the dash. It’s just about doable without removing the glovebox, you’ll need to lie on the sill and bend the underside plastic out of the way, and unclip the wire through the gaps. Two tips here, don’t unclip the airbag if you go down the glovebox removal route, and secondly, you don’t need to remove the three small screws from the blower motor surround. Just twist the blower motor out of the housing. It’s a pain to get back in, you need two hands to get decent purchase, and lie a torch on the carpet.

    Once out, I connected the battery terminals across the blower motor, it pulsed then nothing. Battery showed just over 12v. Have it a minute, then reconnected the hey presto, the blower whizzed round at full tilt. Back in the car, I just connected the cable without putting back into the housing, and with ignition on it whirred again. Hold the bottom of the blower it will jump around.

    This morning it fired up first time. I did stop for fuel five minutes into my journey, and it didn’t come back on straight away, but about 10’minutes later it came to life. All fine this evening too.

    Feels like the 12v shocked it back into life! Worth a try. I’ve comsidered buying a second hand spare from eBay just to rule it out, but I’d perform the same bench test regardless.

    Might be worth a shot! Good luck, and hope this helps! I lost a bit of faith, and was surprised no one else really replied going by the numerous other mentions of similar faults.


    JONATHAN GRAY New Member

    Cheers for the great reply Nick, I've been surprised myself with the lack of info online about the problem. I'll give that a go, have nothing to lose anyway. I've had the problem now for around a month and it's the cold commutes that are forcing me to get my finger out and get it sorted.
    Fingers crossed I'll get lucky with the 12v aswell.

    Thanks again
  7. RichardShute

    RichardShute New Member

    I have precisely the same issue on a 55 plate A6 2.0TDi. Only just fixed the oil pump drive now this Grrrrr.
    The fan had been coming on full blast about 1 minute after starting adn after some manual intervention settled down to normal after waming up. Went to use the car tonight and now it's dead no matter what.
    I need it tomorrow so guess I'll have to just wear thick socks, but will start another spanner session when I'm back.
  8. RichardShute

    RichardShute New Member

    I can now confirm that replacing the fan control unit fixed the problem. It's another contortionists job, but at least it's all from above the engine bay, no grovelling under the dash inside.
    People frequently seem to refer to the thing as the fan "resistor block" but it's a computer controlled power supply vastly more sophisticated and bigger PITA than a resistor block.
    Before getting a new controller I did check the fan and it was OK, and the brushes not badly worn in fact (120k miles on the car).

    At least I now have a spare temporary wiring harness to a simple toggle switch which I duck-taped to the dash. Next time the POS fails I'll add a real resistor and just make the toggle switch permanent.


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