What causes fogging when the car air conditioner is turned on?
2 Answers
Fogging occurs when the car air conditioner is turned on mainly because the air conditioner wind blows on the glass, causing the glass temperature to drop too low, which leads to the condensation of high-humidity outside air on the glass surface. The solution is to avoid directing the air conditioner vents towards the glass. Possible reasons include: 1. Excessive humidity inside the car. 2. The airflow through the car's evaporator is too low, and the air conditioner is in dehumidification mode. It is necessary to check if the indoor unit filter and the back of the evaporator are too dirty. 3. The return air filter of the indoor unit is dirty, or the tilt angle of the indoor unit is incorrect, causing the air conditioner to blow out water. 4. The front-to-back or left-to-right tilt angle of the indoor unit is incorrect, preventing the condensation water generated on the surface of the indoor unit heat exchanger during air conditioner operation from flowing into the water tray in time, forming tiny water droplets that are blown out by the wind.
I've been driving for over twenty years and have seen too many cases of windshield fogging when the air conditioning is on. The most common scenario is when there's a significant temperature difference between the inside and outside of the car—hot glass meeting cold air causes condensation, like when you start the car after a summer downpour. Air conditioning settings can also be an issue, such as using recirculation mode continuously, which traps humidity inside the car. Normally, you should switch to fresh air mode or press the defog button, setting the fan speed higher to quickly dehumidify. Also, keep an eye on whether the cabin air filter is dirty; replacing it regularly can reduce this problem, otherwise dust blocking the vents makes fogging more likely. If you encounter fogging, don’t panic—find a safe place to pull over and adjust the settings. Keeping a clear view is the most important thing. Remember to do a thorough check before the rainy season to save yourself a lot of trouble.
