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De-misting problem

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by Stew2508, Nov 13, 2017.

  1. Stew2508

    Stew2508 New Member

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    Hi all. So just bought my first MB on Saturday, a beautiful 2011 C220 CDI Blueefficiency Sport. However I've got bit of problem with it. The left side of the windscreen mists up and doesn't clear. It's extremely weird as the right side is completely clear. I've tried about everything possible to clear it up such front windscreen demister, recirculation, hot and cold, a/c on and off, Windows down etc.... But nothing clears it. Has anyone else experienced this?

    Thanks in advance.
     

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  2. Rotorhead500

    Rotorhead500 Senior Member

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    Welcome!

    May be worth checking all drains in front of the windscreen are clear on that side (in the black scuttle panel). Is there any damp on the carpets in passenger footwell?
     
  3. bembo449

    bembo449 Senior Member

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    could it need a new pollen filter too perhaps ?
     
  4. L John

    L John Senior Member

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    You either have poor/no airflow on the passenger side screen vent or you have moisture coming in at that side.
    First thing is to check the airflow at the normal side and problem side. Use anything that wags in airflow to compare.

    There are several electrically operated vent flaps behind the dash, my bet is one of the vent flaps is stuck in the closed position.
    Unless it was a private sale, sold as seen, you should be taking it straight back to the seller to let them sort it out. There should be no problem as it's a dangerous vehicle if your screen is obscured with condensation and cannot self clear.
     
  5. OP
    Stew2508

    Stew2508 New Member

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    Thanks I will check it out and get back to you and let you know what I find. I will also give the dealer a call and get them to have a look at it.
     
  6. OP
    Stew2508

    Stew2508 New Member

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    So, I've checked the carpets around the passenger side and they are bone dry, I've checked the drain holes on the windscreen tray and those are clear. I took off the box by the passenger side blower under the bonnet and there is no side of water in their as it is bone dry. I haven't checked the pollen filter as I don't know where it is located. Anything else I can check before getting it back to the dealer on Saturday? Thanks
     
  7. OP
    Stew2508

    Stew2508 New Member

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    Oh the air flow seems OK as well by the windscreen so I don't think the vents are stuck closed. Thanks
     
  8. L John

    L John Senior Member

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    No water anywhere and good airflow on both sides?
    I'd be interested to hear the outcome of this one.

    In the meantime aircon will reduce the moisture content of the air to at least minimise the problem until its sorted. Don't use recirculate, you need fresh air coming in but if that was the issue you would have the problem on both sides.
     
  9. LostKiwi

    LostKiwi Senior Member

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    Misting occurs when relatively warm moisture laden air hits a colder surface. Cold air can retain less moisture so the excess moisture condenses onto the cold surface. Using the demisters increases the temperature of the glass reducing the ability for misting to occur and using the aircon in conjunction reduces the moisture content of air flowing past the screen.
    Therefore for misting to occur you either have excessive moisture on that side of the car (water somewhere in the air stream), ineffective heat on that side of the screen, ineffective aircon on that side of the screen or ineffective airflow.
     
    Last edited: Nov 14, 2017
  10. malcolm210

    malcolm210 Senior Member

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    Check that the windscreen hasn’t been replaced recently they are notorious for this sort of problem if they aren’t 100% sealed
     
  11. John Laidlaw

    John Laidlaw Senior Member

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    ^ what he said ! Try cracking the front window open slightly whilst demisting until you get to the bottom of the problem...
     
  12. oigle

    oigle Senior Member

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    That would depend entirely on what the weather was like outside. If rainy, use recirc, if fine, use fresh. No point in allowing moisture laden air to enter the system.

     
  13. L John

    L John Senior Member

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    No, never to use recirculate in an attempt to clear the screen whatever the weather, if it's already fogging up recirculate would be the worst thing to do.
     
  14. umblecumbuz

    umblecumbuz Senior Member

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    .... and the pollen filter will affect both sides of the screen equally.

    This has to be a stuck ot inop directional flap somewhere, or residual water on that side of the system. Possibly leaving the system on full blast for an extended period might help clear any excessive moisture?
     
  15. LostKiwi

    LostKiwi Senior Member

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    OP, do you get heat out of the left side demister vents?
     
  16. oigle

    oigle Senior Member

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    Please explain reason for your statement....
     
  17. LostKiwi

    LostKiwi Senior Member

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    The quickest way to do it is as follows:

    • Defroster fan on highest setting
    • Temperature control on its hottest
    • A/C turned on
    • Recirculate turned off
    • Crack your windows open 1/2 " or so
     
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  18. oigle

    oigle Senior Member

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    Totally agree except for when it is raining outside as I said before. This video was on the premise of outside air being fresh and dry, if you listen. No value at all in bringing saturated air inside and then having to dry that too....
     
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  19. umblecumbuz

    umblecumbuz Senior Member

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    Ahh ... but does aircon work as well when recirculating cabin air?
    If so, it would continue to remove moisture from the air with all windows closed, resulting in desert-dry fug as opposed to jungle-humid fug.
     
  20. Frontstep

    Frontstep Senior Member

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    Mt fug goes through carbon filters so its pretty clean and dry fug.
     

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