Fogging within a windshield vapor occurs when water from inside the warm car condensing on the cold windshield. The air in the car absorbs moisture from the exhaled breath of the passengers or any wet clothes. If the heating is turned on, the air in the car heats up, absorbing more water vapors. When moist air that touches the cold windshield, it cools and becomes supersaturated, and the water vapors condenses. If the windshield is sufficiently cold, condensation can become ice. This creates a potentially dangerous situation because fogging or freezing on the windshield limits driver visibility. There are several steps you can take to limit the effects of condensation on the windshield.
- Direct warm air using the setup windows defrosting, as the windshield is heated, there is less temperature difference between it and the air in the car, so it is less likely that condensation occurs.
- Deactivate the air recirculation control. Air recirculation helps to quickly re-heat the car, but also increases the humidity inside the car, passing air through it and again, absorbing more moisture from occupants. Since cold air support less moisture than warm air coming from outside will be less humid than warm inside, even if it is raining or snowing.
- Turn on the air conditioning. The compressor removes moisture from the air inside the vehicle, so that air hits the inside of the windshield is less humid because is supersaturated.
- Remove the rain or snow before entering the car. The additional water in the car increases the humidity, so do everything you can to limit the amount of water entering the car. When possible, shakes umbrellas, coats and boots out of the car. Do not leave open containers of fluids in the car. If the seats are wet, wipe the moisture as soon as possible. Do not leave wet rags or other items in the car.
- Clean the windows with an ammonia-based cleaner or shampoo. There are also liquid treatments and commercially available towels specifically designed to deal with windshield fog and condensation.