# Dehumidifying a Car?

**URL:** <https://boards.straightdope.com/t/dehumidifying-a-car/151887>\
**Category:** In My Humble Opinion\
**Created:** [January 31, 2003, 4:31pm UTC](https://boards.straightdope.com/t/dehumidifying-a-car/151887 "2003-01-31T16:31:50Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Rubystreak](https://avatars.discourse-cdn.com/v4/letter/r/e5b9ba/32.png) [@Rubystreak](https://boards.straightdope.com/u/Rubystreak)\
**Post date:** [January 31, 2003, 4:31pm UTC](https://boards.straightdope.com/t/dehumidifying-a-car/151887/1 "2003-01-31T16:31:50Z")

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I have a Toyota Camry that just has this hideous problem with humidity: the windows always fog up if they’re closed, and frost forms on the insides of windows in the winter. Also, the doors retain water and then freeze, sometimes shut.

Does anyone know a good way to dehumidify a car? And what causes a car to retain moisture like that? I park it on the street, not in a garage, but I don’t notice any of the other cars on the block being so frosty (or dew-covered in warm weather).

Thanks.

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**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\
**Post date:** [January 31, 2003, 5:03pm UTC](https://boards.straightdope.com/t/dehumidifying-a-car/151887/2 "2003-01-31T17:03:12Z")

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Ah, a toyota design issue. There was another topic on this on the board with the exact same thing happening. You might search for it but it appears you need to turn on the air conditioner to clear the windows, odd eh? You’d think that Toyota would know better.

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**Author:** ![PumiceT](https://avatars.discourse-cdn.com/v4/letter/p/43a26b/32.png) [@PumiceT](https://boards.straightdope.com/u/PumiceT)\
**Post date:** [January 31, 2003, 5:35pm UTC](https://boards.straightdope.com/t/dehumidifying-a-car/151887/3 "2003-01-31T17:35:29Z")

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Yeah. A/C doesn’t simply cool air, it shoots out dry air. Turn the A/C on with your heater, and you’ll be golden.

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**Author:** ![Rubystreak](https://avatars.discourse-cdn.com/v4/letter/r/e5b9ba/32.png) [@Rubystreak](https://boards.straightdope.com/u/Rubystreak)\
**Post date:** [January 31, 2003, 6:09pm UTC](https://boards.straightdope.com/t/dehumidifying-a-car/151887/4 "2003-01-31T18:09:48Z")

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OK-- now, do I leave the vents open or shut when I do this? Will this help only when I’m driving? In the morning, it’s a huge pain in the ass to have to scrape down BOTH sides of the windows.

Is there some sort of chemical dehumifiying thingie (I believe that’s the scientific name for it) I can put in the car?

Thanks, guys. I appreciate your help on this.

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**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\
**Post date:** [January 31, 2003, 6:24pm UTC](https://boards.straightdope.com/t/dehumidifying-a-car/151887/5 "2003-01-31T18:24:27Z")

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Make sure the system is **NOT** in the “recirculate” position. Use recirc only for coldest air conditioning, not for vent, heat, or defrost.

As mentioned, use A/C with the defroster (A/C dehumidifies). A properly working heater will more than compensate for any slight additional cooling.

Have the car checked for a blocked evaporator drain hose, which could trap moisture in the ductwork.

Have the car checked for a leaking heater core.

Check for any sign of moisture in the floorboard area, under the carpet.