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W163 Front screen demist

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by TechnoWhizz, Dec 29, 2017.

  1. TechnoWhizz

    TechnoWhizz Active Member

    Messages:
    27
    Likes Received:
    3
    Joined:
    Mar 18, 2016
    Location:
    Rugby
    Your Mercedes:
    ML500 W163 2003 Black LPG
    On my W163 2003 ML500 with LPG conversion.... The front screen demist isn't working. On auto or manually select or Demist button, the fan is working fine, but the flap doesn't seem to open. I've tried moving the direction control and you can hear the flaps moving, but no air to the screen. Also the air is blowing very cool even when the engine is hot @80c. I'm not overly bothered about the heat as I've already tried a Mercedes specialist who was useless in sorting it, but getting the flap to move would be great, even if it's permanently open. Are the temp/vent controls electric or cable operated? Is there a temp mix valve I can check?

    Any ideas where to look or is it a dash out adventure?
     
  2. brianbrian

    brianbrian Senior Member

    Messages:
    2,744
    Likes Received:
    178
    Joined:
    Sep 27, 2008
    Location:
    cockney in the West Country
    Your Mercedes:
    w124 250D, SL129-deisel
    I would change engine thermostat first to get rid off windows steaming up, and engine reaching proper temperature, also check under carpets for wet or damp.
     
  3. range rover

    range rover Senior Member

    Messages:
    577
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    65
    Joined:
    Mar 26, 2008
    Location:
    Northern Ireland
    Your Mercedes:
    E Class Blue EFFICIENCY 250 CDI Sport 2013
    There is an item called a 'duovalve' which may be the culprit, I know nothing about your model, but in my car it is fitted in the bulkhead, even giving it a sharp tap may do the trick. I had mine replaced a few years ago, also as above, your thermostat seems to be playing up,90c is the normal working temperature.
     
  4. Brian23

    Brian23 Senior Member

    Messages:
    1,392
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    Joined:
    Jan 11, 2008
    Location:
    UK
    Your Mercedes:
    EClass
    Hi I had the same problem with my E200 and in my case it was the duovalve, as above. During the summer when it is not in use it seizes up. There are a few threads on here about them. As a temporary fix you can, as said above tap with something to free it, but if this is happening it should be changed. I bought a new one with the intention of changing it, but on my car it is in such a awkward position that I have not done it yet and as yet it is still working, as this summer I put the heat on full for a few minutes when I thought about it, to keep the valve from seizing. You can also tell that it is this because IF you can locate the valve, the water pipes one side are hot and the other cold as the valve is stuck. If your temp gauge is showing hot, it is unlikely to be the thermostat. Also see my thread.
    http://forums.mercedesclub.org.uk/index.php?threads/2005-eclass-heater-not-working.147516/
     
    Last edited: Dec 30, 2017

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