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W124 Coupe Heater - Help!

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by Mercky, Oct 22, 2012.

  1. Mercky

    Mercky Senior Member

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    Joined:
    Aug 30, 2004
    Location:
    Dublin, Ireland
    Your Mercedes:
    96 W124 320 Coupe
    Hi All,
    Can somebody kindly give me some guidance, the heater in my 96 124 coupe is acting up and the passenger side goes cold after about 20 mins regardless of dial setting. The car has AC and this behaves the same when switched on. When I turn dial all the way up to the click or 'demist' it's fine and throws out great heat. Driver side is fine and works perfectly. I suspect that perhaps the temp sensor is gone on the passenger side and I was going to swop around the connectors to see if the fault followed. Yesterday after studying the fairly useless Haynes Manual I removed the fascia and the heater matrix panel no problem but theres a switch holding bracket behind which I cant seem to get out - I'm presuming the sensors are behind it going by the manual? Can anybody advise as to how to remove this switch holder (i dident want to force it) and am I right in terms of suspecting the sensor or could it be the dial / matrix itself or a dodgy duo valve?? Any thoughts and advice welcome.

    Thanks in advance

    Mercky
     
  2. television

    television Always remembered RIP

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    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    The duo valve sir 53

    [​IMG]
     
  3. OP
    Mercky

    Mercky Senior Member

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    Your Mercedes:
    96 W124 320 Coupe
    Thanks Malcolm, you seem pretty confident! Can I reverse the connector to the duovalves to see if problem reverses also, I know the connector is keyed to only go in one way but if I overcame that is it a worthwhile check?
     
  4. television

    television Always remembered RIP

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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    You can do that no problem,,, the center pin is common.

    You can apply 12volt to each valve in turn and feel the clonk, also when working correctly you can feel the pulse from the control unit.

    The output from the control puts out about 11 volt (pulsed) but it can be read on a normal meter
     
  5. kth286

    kth286 Senior Member

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    Your Mercedes:
    E320 Coupe 95
    duo valve failures usually default to the 'hot' position, so I would say unlikely
    to be that.
     
  6. television

    television Always remembered RIP

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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    Yes this is what has been said, but my 140 failed in the cold position, so we may have to discount that
     
  7. OP
    Mercky

    Mercky Senior Member

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    Your Mercedes:
    96 W124 320 Coupe
    OK so I reversed the connector to the Duo valves and now the drivers side cools and the passenger side is correct - the exact reverse of before so its not the Duo valves!!
    I presume now its either the dial control itself or a temp sensor? I was thinking as a temporary cheap fix I could, on the duo valve connector, short the wire from the good side (drivers side) to the pin on the duo valve for the passenger side so now the dial for the drivers side controls both valves and just use one dial for the present??
     
  8. television

    television Always remembered RIP

    Messages:
    164,074
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    Joined:
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    Location:
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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    What heater control do you have, the switches can get dirty giving poor contact

    As before the control panel gives out 0 to 11 volts, is there any voltage on the one that is not working
     

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