What Causes Fogging on the Outside of Car Windows in Summer?
2 Answers
In summer, car windows fog up due to the low temperature setting of the air conditioning inside the car, which creates a significant temperature difference. The interior of the car is cooler, while the outside temperature is higher. When the hot outside air comes into contact with the cold glass, the water vapor in the outside air condenses into tiny droplets on the cold glass, forming what we commonly refer to as fog. Reasons for car window fogging in summer: The cold air blown out by the AC lowers the temperature of the glass area significantly. When this cold glass encounters the warmer outside air, especially in conditions of high humidity, it easily forms a layer of fog on the outside. Using the AC to remove fog: For manual AC models, simply turn the fan speed to the maximum, turn on the AC's A/C switch, set the temperature to the lowest, and press the front window defogging button. You will see the fog on the windows gradually dissipate. For automatic AC models, press the AUTO button, set the temperature to the lowest, and press the front window defogging button. For models equipped with rear window heating and defogging functions, pressing the rear window defogging button can speed up the defogging process and help prevent fog from forming again. Using professional defogging agents: Before applying the defogging agent, clean the inside of the windshield thoroughly. Spray an appropriate amount of the defogging agent, let it dry, and then wipe it off with a clean towel. The defogging agent creates a hydrophobic layer between water molecules and the inner surface of the glass, keeping the glass surface clean and preventing fog formation.
Fogging on the outside of car windows is most common in summer. I used to encounter it frequently while driving, especially after rain or when the air conditioning was just turned on. The key reason is the high humidity in the outside air, such as on rainy days or after rain. The car glass gets too cold from the air conditioning, and when the warm, moist outside air hits the cold glass, it condenses into tiny water droplets, just like water droplets forming on an iced glass. At this point, visibility becomes blurry, making driving particularly unsafe. I always make it a habit to either turn up the air conditioning temperature or adjust the airflow direction upward to avoid direct cooling of the glass, or simply use the wipers to sweep it away, which works quite well. Another factor is dirty or oily glass, which makes it easier for water fog to stick, so I regularly clean the glass. This happens more frequently during the high-temperature summer season, so I recommend keeping a clean cloth in the car. When fog appears, just wipe it off—don’t wait for an accident to happen before dealing with it.
