Defog Windshield without dehumidifying

Discussion in 'Gen 3 Prius Technical Discussion' started by FrugalBeeotch, Nov 20, 2025 at 10:17 AM.

  1. FrugalBeeotch

    FrugalBeeotch Junior Member

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    2013 Prius Plug-in
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    I have a 2013 Prius Plug-In. I live in PNW, so it is very humid in the winter, but also cold. I've noticed if I try to defog my windshield, suddenly very cold, dry air is coming from those vents and it feels like the A/C is on, as it immediately kicks on the IC engine. When the windshield is defogged, I switch it to blow out the vents to warm me and the pup, but suddenly it blows out all the humidity that was in the A/C coils, and I'm back to a foggy windshield.

    So here's my question: is there a mode, or a setting, where I can defrost the window with only heat (no dehumidifying)? I absolutely hate having the A/C running in the winter. It dries my sinuses and causes me all kinds of trouble.
     
    #1 FrugalBeeotch, Nov 20, 2025 at 10:17 AM
  2. BiomedO1

    BiomedO1 Senior Member

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    2021 Prius Prime
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    LE
    The quick answer is NO. Warm humid air recirculating around will simply lead to refogging of the glass. Add to that the air you and your pup are exhaling into an enclosed space with cold glass all around you. It's a lot worse than a foggy bathroom mirror because the other sided of the glass is much colder. It's simple physics - same reason a cold beverage glass sweats.
    Bottom line; you need to lower the humility of the air within the cabin to keep the glass from refogging.

    YMMV
     
    #2 BiomedO1, Nov 20, 2025 at 12:19 PM
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