Ice forming inside



Why does ice form inside the windshield sometimes during the winter? How can you keep this from forming or get it off easily (since normal ice scrapers are curved the opposite direction)?


Turn on your defroster and A/C. This seems contradictory, but the heat from the defroster and the drying effect of the AC work to quickly remove condensation or ice on the inside of your windshield. Or, stop breathing.



High moisture content inside. If it seems worse than normal, you might have leak in heater core. As twotone says, if it’s just occasional, deal with it that way.


Around here, ice inside the windows typically happens when a mild, moist airmass that brings rain is followed by a cold, Arctic air mass. The water vapor (humidity) is trapped in the car and when the temperature drops far enough, it forms ice on the inside of the windows. If your car doors are prone to freezing shut, that’ll happen also.

The cure is to ignore all the advice you hear from self appointed experts about not warming up the car. Start the car, set the heater to defrost, and let the car idle until the windows clear. Once you have the windows clear, open the doors for a minute or so and let the cold and very dry outside air replace the now rehumidified inside air. The air conditioner is supposed to handle the latter job, but I suspect it does a lot better job of dehumidifying in San Francisco or New Orleans in Summer, than in the Northern states in Winter.

On most cars, you can try mechanical scrapping on the front windows instead or as well if you can find a scraper that works on the surface. Don’t use it on the rear window. You’ll probably scrape the wires for your radio antenna and electrical rear window defroster right off.


If it’s a wet, sloppy and cold day, I use the climate setting where the air is blowing at the person’s feet but then the winshield defrost icon is right in front of the person’s torso.

It runs the compressor a little bit (good for it in the winter, keeps your a/c in shape) and dehumidifies the interior of the car. This works for me pretty well. Try it.


At last, a practical approach.


When you shut off a warm car with losts of moisture inside from snow and slush, and park it in a cold area, the inside window will be frost covered by morning. This happens all over the world, not just in your car.

As pointed out, you need to drive off that moisture and the defroster and A/C settting (on many cars it comes on automatically) will evaporate this ice quickly. I keep a small hand scraper around as well and scrape SIDEWAYS to get most of the ice off.

This is one instance where we would recommend you do not drive off immediately , for your own safety.


If your vehicle somehow automatically sets the air on recirculation, then that might be another cause.
I’ve had this happen to me a couple times where I’d set the temp and fan speed when I get out of the car in the afternoon and I know it’s gonna be cold in the morning. I set it so I can just use my remote starter and let it sit for a couple minutes while I finish getting ready for work. When I set the “recirc” button a time or two, I’ve had the ice on the inside of the window, and nothing on the outside.


A truely outstanding explanation with usable advice to boot!

Nice post.