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Air con not working - advise needed

Discussion in 'A6/S6/Allroad forum (C5 Chassis)' started by Omniquito, May 12, 2013.

  1. Omniquito
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    Omniquito Member

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    [May 12, 2013]
    Hi guys,

    I know there are a few posts on this but I cannot find my specific issue.

    The fan isn't working, I had it regassed, it had pressure in so there is no leak but that didn't sort it, I have checked the fan and that is ok and the 40amp fuse is ok, what else could it be?

    I have heard it could be one of a couple of temp sensors, but I am not sure what ones and more importantly where they are?

    I have a vag com free version but got no codes from it so assume I am not doing that correctly...

    Please help!
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  3. wesmaster
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    [May 12, 2013]
    Have you checked the compressor clutch electrically and mechanically?
    #2
  4. Omniquito
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    [May 12, 2013]
    No I haven't, wouldn't know where to start on that one :-/
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  5. TYphoon GB
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    [Jun 2, 2013]
    This is all a lot easier with the front off.
    First you need a manual or ElsaWin to find all the bits (ebay about £5)

    The air con needs the compressor, LP switch, fans and control unit to be working.
    Is there a red light on under your ECON button?

    You will need a multimeter or at best an indicator bulb and some wire!

    Power needed to the fan controller.
    Power needed to the fan
    Power needed to the compressor to operate the electric clutch that drives the compressor
    Signal from the LP switch (behind front bumper)

    Option one is you have a massive hole (1mm or so) and the refrigerant pressure is dropping so quickly the LP switch turns off the power to avoid dry running the compressor. Condenser is the main failure as it takes all the stone chips.

    Next check the belt is still on. Just had a car following a cam belt change the they left the belt off FFS.

    The LP switch can work loose (its on a schrader valve) and can fail. Cheap ebay ones work OK.

    Fans can fail...worth a quick check

    Fan controller can fail again a quick check (PITA to get to)

    Lastly compressor failure....rare but there are are plenty of s/h ones out there.


    Compressor black thing bottom right

    [​IMG]

    Condenser damage

    [​IMG]

    Temperature sensor

    [​IMG]


    LP switch/Pressure Sensor (LHS of condenser)

    [​IMG]

    If you have refrigerant pressure (LP switch sends power to the fan controller) then its electrical.
    #4
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  6. Omniquito
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    [Jun 2, 2013]
    Wow!, that reply is absolutely fantastic, thank you so so much!

    I only have the red light on the econ mode when you press it, there is pressure in the system as I had it regassed and they said it still had pressure in before they drained and regassed so think the condenser should be ok, will start looking into the other stuff tomorrow.

    I don't fancy removing the front end but will get elsawin and see what it entails.

    I will keep you updated and thank you so so much for your absolutely awesome post, I wish the world was filled with people like you :)
    #5
  7. TYphoon GB
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    [Jun 3, 2013]
    Careful what you wish for...but thanks anyway...
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  8. Omniquito
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    [Jun 3, 2013]
    Lol that is fair enough!

    Is it worth investigating the sensor if I don't get the econ light on full time? it comes on when you press the econ button but goes off when you press auto?

    Also, I have heard a rumour that there are other fuses to check out too apart from the 40amp ones, is this true? someone said something about a 5 amp fuse that protects the sensor?
    #7
  9. TYphoon GB
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    [Jun 3, 2013]
    The red light signals ECON on and low pressure so if its off your pressurised and the sensor is working.
    Model specfic fuses and relays but yes you need to find and check them all.

    I will check on my copy of Elsa tonight.... what model/year?

    Does your cooling fan run OK

    Does the fan run as the A/C comes on.

    Does the A/C click or clunk if you slowly switch the ECON off and on?

    If you can get access to Vag Com / VCDS the sensor and motors will throw a fault code...might be quicker?
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  10. Omniquito
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    [Jun 3, 2013]
    Hi :)

    I have a copy of elsa win coming but as this heat I need to fix ASAP! Lol

    The one thing that is missing is the tell tale click and rpm drop (slight) when the air con kicks in. The fan does NOT come on so will go for the other fuses and if I can find the fan plug then see if it is getting power maybe, the fan moves freely by hand so no jam...
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  11. Omniquito
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    [Jun 3, 2013]
    Sorry, forgot to say it is a 2003 Audi allroad 2.5tdi :) please help with the fuses.
    #10
  12. TYphoon GB
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    [Jun 3, 2013]
    Side fuse panel
    Micro relay panel (under drivers storage compartment)
    Relay Panel in Lower A Pillar.

    Drop some diagrams in later...
    #11
  13. Omniquito
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    [Jun 3, 2013]
    Thank you, with the diagrams i will bell them all out tomorrow.
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  14. TYphoon GB
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    [Jun 4, 2013]
    So there is a small fuse on the relay panel...

    [​IMG]

    J44 and N25 are the key items

    [​IMG]

    [​IMG]

    Just noted you used Vag Com and no faults?

    So I'd look at fans and fan controller power...

    AudiWorld Tech Articles
    Last edited: Jun 4, 2013
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  15. Omniquito
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    [Jun 4, 2013]
    Hi there,

    I have a VAG COM but never used it before (think its the free version) and although I followed the instructions to scan it seemed to do with nothing appearing at the end.. I know this may sound dumb but I assumed that if there were no error codes then it would tell me and not simple display nothing?

    Anyways... I checked all fuses and they seem ok, I got to the fan wiring and tried poking 12v down the ac fan and nothing... I then measured resisitance across the fan terminals (pos and gnd) and open circuit... Is there a controller on the fan that would display open or is this the sign of broken fan?

    Curiously I powered the car up, put all heater controls to LO and the only voltage I get going to the fan is 1.2v even after a couple of minutes of running when I would expect it to be fully powering the fan...

    Also, if it was just the fan would I still hear the compressor and relays still clicking and engaging?

    Over to you mate, I am stumped...

    Thanks again for your amazing help and effort...

    PS... looking deeper, I could be being a dumbass here, are those both power wires and not power and gnd? this could be embarrassing! lol
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  16. TYphoon GB
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    [Jun 4, 2013]
    First fix your Vag Com......it should run a full scan module by module and display all the results OR go to the Air Con module and scan.

    Fan is + and -ve.....without the fans the controller wont power the compressor relay.

    There is no controller on the fan (that I am aware of).....

    This may help

    [​IMG]
    #15
  17. Omniquito
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    [Jun 4, 2013]
    Hmmm... this is doing my head in! lol I think I maybe rapidly getting out of my depth with these wiring diagrams...
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  18. TYphoon GB
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    [Jun 4, 2013]
    More specific...

    12V on V7 should make it run...

    [​IMG]
    #17
  19. TYphoon GB
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    [Jun 4, 2013]
    Oh did you check the Audiworld Tech Articles link?
    #18
  20. Omniquito
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    [Jun 4, 2013]
    Yes that was good to see, I applied 12v to the fan and no go so pretty sure this is the problem. I will look to see if I can test the controller, still not sure why I only get 1.2v at the fan plug though... maybe that is a sign of a dead controller too... seems odd that fan and controller have gone.
    #19
  21. TYphoon GB
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    [Jun 4, 2013]
    More likely the S142 fuse than the controller.

    But if 12v don't get the fan running.....the high and low speed is worked by switching power through the resistor.

    Again Vag Com might help...does the Test function work on that (under Options)?
    #20
  22. mwarrey
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    [Jun 4, 2013]
    If the fan doesn't work with 12v directly to the terminals, its certainly the problem. I had the same issue with mine. There are is a fan output test on VAG COM which you can also use. I have a write up on how to change\repair the fan which I can email you if you PM me your email.
    #21
  23. Omniquito
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    [Jun 6, 2013]
    Still working on the vagcom :(

    After closed inspection fuses are all ok and found them all too! Lol

    I have 7.5v going fan so I am assuming that the controller is ok and this is merely a low speed voltage... Is this true?
    #22

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