Why does turning on the AC cause fogging?

[GabriellaDella]

Fogging on the windshield when the AC is on occurs due to a significant temperature difference between the glass surface and the interior air. The high outside temperature contrasts with the low interior temperature, and the windshield, which separates the inside from the outside, also remains cold. When the humid air inside the car meets the cold windshield, it condenses into water droplets that adhere to the glass, severely impairing visibility. During rainy or foggy weather, the air humidity is higher, increasing the moisture inside the car and making condensation into fog more likely. Solutions for fogging on the windshield when the AC is on: 1. Open the windows: If the fogging is not severe, slightly opening both side windows can promote air circulation. 2. Turn on the heater: Blowing warm air can fundamentally solve the fogging issue. 3. Use anti-fog spray: Applying a layer of anti-fog spray on the windshield prevents water vapor from condensing.