What Causes Window Fogging?
3 Answers
Window fogging in winter and summer is caused by significant temperature differences or humidity variations between the interior and exterior environments. Defogging methods: 1. Manual air conditioning: For vehicles equipped with manual air conditioning, you can activate the front window defogging mode, set the fan speed to maximum, turn on the A/C switch, and adjust the temperature to the lowest setting to dry the fog on the windows. 2. Automatic air conditioning: For vehicles with automatic air conditioning, simply pressing the one-touch defrost button will quickly eliminate the fog. If the ambient temperature is too cold for cold air, you can also use the heater by setting the fan speed to maximum and activating the front window defogging mode, which will clear the fog within minutes. 3. Electric heating: Most rear windows come with electric heating. You can directly turn on the rear window and mirror heating functions to quickly remove fog and prevent it from recurring.
Last time I drove my kid to school in heavy rain, the windshield suddenly fogged up and drove me crazy. It's actually caused by temperature difference: when the cabin is warm and meets the cold window, the moisture from our breath condenses like dew on a cold drink cup. Turned on the AC but found it getting foggier? That's because the AC wasn't on, and blowing warm air only made the glass hotter. Add rain outside, and the fog turns into frosted glass. The worst is in winter with the heater on and recirculation mode engaged—seven or eight people breathing in a crowded car can turn the windows into frosted glass in minutes. Now when I wait in the car, I always leave a window slightly open for ventilation, and I keep old newspapers in the trunk for emergency window wiping.
With 13 years of car repair experience, I've seen all kinds of fogging cases, which ultimately boil down to moisture condensing when meeting cold surfaces. In summer, blasting the AC too hard with vents directly pointed at the windshield causes cold air to form condensation on the hot glass. Winter presents the opposite scenario – warm air heating the glass while outside cold air frosts the exterior. Some drivers don't understand the difference between recirculation and fresh air modes, running recirculation continuously during rainstorms which traps all passenger breath moisture inside. Here's a hidden factor: an unchanged cabin air filter for two years becomes saturated with humidity and fails to block moisture intrusion. The simplest solution? Turn on AC dehumidification and set the temperature dial around 22°C for hassle-free defogging.
