What to Do When Car Windows Fog Up?
4 Answers
Here are ways to solve the issue of car window fogging: Press the defog button, turn on the air conditioning (A/C) switch, and activate the external circulation to remove fog. Use the air conditioning's dehumidification function to reduce air humidity and eliminate fog. Reduce the temperature difference to prevent window fogging. Apply anti-fog spray to prevent dirt and stains on the windows. Open the windows to allow air convection between the inside and outside of the car, which will reduce the temperature difference and gradually dissipate the fog. Causes of car window fogging: There is a temperature difference between the inside and outside of the car. If the temperatures differ, the surface with the lower temperature will have a lower saturated vapor pressure than the surrounding environment, causing water vapor to condense on the glass surface in tiny droplets, forming fog.
Fogging on the car's exterior glass occurs due to temperature differences between inside and outside, causing moisture condensation. I usually turn on the AC to defog first: set the AC to external circulation, adjust the temperature to cool or medium (not too low to prevent frost), and increase the airflow directed at the windshield—the fog clears in seconds. Remember to turn on the fan to assist and speed up air circulation. If your car has a rear window heating function, press the snowflake button as well. To reduce the chance of fogging, avoid drinking hot beverages or placing wet items in the car before driving. If fog has already formed before heading out, gently wipe it with a soft cloth or use the wipers lightly to avoid scratching the glass. Cold cars in winter mornings are prone to fogging, so turn on the AC to defog while warming up the engine. If fog suddenly appears while driving, don’t panic—slow down, pull over safely, and handle the situation before continuing.
Dealing with foggy exterior car windows is quite simple. I immediately turn on the air conditioning in dehumidification mode: set the temperature to a moderate level, direct the airflow toward the windows, and turn on the fan along with the external air circulation. When there's a significant temperature difference inside the car, moisture condenses into fog, but the air conditioning's drying function quickly absorbs the moisture to resolve the issue. If the rear window has a heating wire, just press the button to warm it up and melt the fog. While driving, keep the internal air circulation off to reduce humidity buildup, and leave a small gap in the window for ventilation. Preventive measures are crucial, such as keeping the windows clean—dirt accelerates fogging—and avoiding excessive use of cold air in humid summer weather to prevent worsening temperature differences. For tools, keep a window defogging spray handy; spraying it forms an anti-fog film, clearing the window in seconds. Safety comes first—if fog obstructs your vision, don't push through; pull over and handle it promptly.
For foggy exterior glass, I directly operate: start the car, turn on the air conditioning with cool air blowing on the glass, combined with opening the window for ventilation, and it will be done in minutes. Fog mostly occurs because the warm air from breathing inside the car meets the cold glass, and introducing dry air through the external circulation is most effective for dehumidification. If the fog is heavy before getting in the car, wipe it with your hand or a cloth, but don't use too much force. For regular maintenance, apply anti-fog spray or coating to the windows to prevent fogging. If fog occurs while driving on the highway, use the wipers as an emergency measure, but don't use them frequently as it will wear out the wiper blades. Adjust habits to prevent fogging during significant weather changes, such as promptly removing accumulated water after rain to reduce humidity. Slow fog removal can distract and increase the risk of accidents, so don't take it lightly.
