What causes fogging when the car air conditioner is turned on?

[CharlieFitz]

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.

[Dominick]

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.

[RiverAnn]

As someone who drives to work every day, I've recently found it quite annoying when the windshield fogs up after turning on the AC. The main reasons are setting the temperature too low or improper switching between internal and external air circulation, causing moisture to condense on the glass. I usually manually increase the fan speed to blow air towards the windshield, which clears the fog faster. Additionally, if the car's AC filter hasn't been replaced for a long time, it can absorb moisture and worsen fogging. It's recommended to clean it with a vacuum cleaner every month. When driving in dry weather, turning off the AC for a few seconds before switching to external circulation can balance humidity and reduce fogging. Make it a habit to check the settings before heading out in the morning to ensure safe driving—small fog issues can lead to big problems.

[DelReid]

As someone who frequently drives long distances, I find that the windshield fogs up quite often. A significant temperature difference causes condensation on the glass, especially during rainy or snowy weather, or when starting the car after parking. Simply put, the temperature difference between inside and outside leads to moisture condensation. In terms of operation, I usually turn on the external circulation mode immediately after starting the car, increase the fan speed, and direct the airflow toward the windshield. Doing this consistently can help avoid fogging issues. If the air filter is dirty, it should be replaced; otherwise, the problem worsens. Don’t overlook interior cleanliness—wiping dry any water stains on the dashboard can also reduce moisture buildup and fogging. Maintaining clear visibility is crucial for driving safety.