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Poor Deforst Perfomance

Discussion in 'Model X' started by K-MTG, Jun 24, 2017.

  1. K-MTG

    K-MTG Sunshade Captain of TMC

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    IMG_2158.JPG After leaving my car outside at night for a few hours, I develop some moisture on the windshield, typical in all cars. However, I can't get it to clear fully, it will slowly disappear when I drive highway speeds but it returns when I am back on the street. I turned on the deforst (blue) and increased fan speed but that didn't help.
     

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  2. mongo

    mongo Member

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    Is the moisture on the inside or outside of the glass? I get that on the outside on humid days when the AC cools the windshield below the dew point (non-Tesla).
     
  3. K-MTG

    K-MTG Sunshade Captain of TMC

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    I am not sure but it occurs where the defrost vents are located
     
  4. hiroshiy

    hiroshiy Supporting Member

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    If your AC blows colder air than ambient, you will get fog outside of the front window. That can only be cleared with wipers. Isn't that the case?
     
  5. K-MTG

    K-MTG Sunshade Captain of TMC

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    The wipers didn't remove that
     
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  6. TLej

    TLej Little-Known Member

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    I think it comes down to humidity. I don't use any of the auto settings and I'm not sure what the blue defog is doing, but I would check and see if it turns the AC on and if it's set to recirc or fresh air. You want AC on and set to recirc, if I recall correctly. Temperature doesn't need to be low with AC on, the AC just de-humidifies the air.

    You could also try this video and see if it helps: Fastest Way to Defog Windshield

    Edit: the owner's manual is not very helpful, but it does mention the fresh air setting to be more effective in dehumidifying, so try it with AC on and ventilation set to fresh air.
     
  7. X Fan

    X Fan Supporting Member

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    The reason is apparent: you didn't use an overnight sunshade.....
     
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  8. TallPaulS

    TallPaulS Member

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    So toward the end of winter I was driving down the highway and had a bit of frost building up (perfect combination of humidity and temperature) so I hit the defroster and nearly had a heart attack when nearly the whole thing went white within a few seconds. I then learned about hitting the defroster twice (red) which clears the windshield like a charm. But boy was that scary.
     
  9. K-MTG

    K-MTG Sunshade Captain of TMC

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    I tried that but it didn't help, just made the car very hot. It's like 80 degrees at night in SoCal these days
     
  10. deerfield

    deerfield Member

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    Make sure range mode is not on. I find that it significantly reduces defog functionality.
     
  11. hiroshiy

    hiroshiy Supporting Member

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    Wondering where those moisture come from... If it is fogging inside of the window, I can think of a few reasons.
    (1) The windshield has some dust on the surface. Dust is known to collect moisture. If the windshield is clean, it's hard for water to collect on it and fog.
    (2) The water might come from the A/C unit. That means there might be some liquid water inside of your A/C unit. Don't know how to check, but if you have a future opportunity to visit the service center, please ask them to check the A/C unit for any water inside.
    (3) As @deerfield suggested, range mode doesn't use much heat to evapolate water. If the humidity inside your car is high like over 80% (can't believe in CA though), range mode defroster wouldn't be able to clear the fog. Use red mode defroster or turn off range mode. But I think (1)(2) are more likely...
     
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