What to Do When Car Windows Fog Up in the Rain?

[McMadison]

Press the defogger button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and switch to external circulation to defog. Fog on car windows can be cleared using either cold or warm air, but warm air is slower than cold air. The most effective method is to use cold air, which blows dry, cold air directly onto the glass, preventing water vapor from condensing on the surface and achieving defogging. The method for using warm air is the same as cold air defogging, but note that warm air should not be used for defogging on rainy days, as it may initially worsen the fog. Always use external circulation when defogging car windows. The reason car windows fog up: There is a temperature difference between the inside and outside of the car. If the temperatures inside and outside are different, the side with the lower temperature has a surface water saturation vapor pressure lower than the surrounding environment's vapor pressure, causing water vapor to gather on the glass surface and form tiny droplets, resulting in fog.