Why Does the Windshield Fog Up When Using Air Conditioning in Summer?
4 Answers
In summer, when the air conditioning is turned on inside the car, the outside temperature is lower than the inside temperature, causing the water vapor inside the car to form many tiny water droplets. The surface of the windshield is not perfectly smooth and has many small imperfections, so these tiny water droplets adhere to the windshield, resulting in fog formation. Below are some methods to deal with fogging on the car windows when using air conditioning in summer: 1. Use the air conditioning system to remove fog: The air conditioning system can be used to remove fog from the glass in both winter and summer. In winter, turning on the cold air conditioning can effectively remove water fog from the glass. However, in summer, it's not practical to turn on the heating for this purpose. The best method is to switch between the internal and external air circulation to allow better airflow, which speeds up the evaporation of the fog. This can quickly remove water fog from the glass. Additionally, periodically switching between internal and external circulation can help purify the air inside the car, making the ride more comfortable. 2. Apply soapy water: You can apply soapy water to the inside and outside of the windshield and then use the wipers to wipe it off once or twice. The soapy water on the inside of the windshield can be gently wiped with a tissue until it is semi-dry. Once the soapy water is completely dry, the windshield will not fog up. As long as it is not wiped off, this method can generally last for about a week.
I've encountered this issue since the first day I started driving. In summer, the main reason for windshield fogging when using AC is because you set the temperature too low. The cabin air rapidly cools and dries, but the windshield remains heated by the outside sun. When the temperature drops, moisture in the car immediately condenses into tiny droplets on the inner glass surface, forming fog that obstructs visibility. Simply put, it's a temperature difference issue – hot outside and cold inside the car in summer, which easily causes this when humidity is high. When driving, I pay special attention: don't panic when fog appears, slow down and pull over, turn on external circulation for a few minutes to reduce humidity, or use the defog button for quick clearance. Develop good habits: avoid direct AC airflow to the windshield when starting, set moderate temperature (not too low), and regularly clean window stains to reduce fogging probability. Safety first – obscured vision easily leads to accidents, so I always remind beginners not to skip preventive measures.
In the scorching summer heat, turning on the AC feels refreshing, but the foggy windshield is a real nuisance. I often find myself driving with a blurry view of the road. The reason is that the cold air from the AC hits the glass, cooling it down, while the high humidity inside the car causes moisture to condense into droplets on the cold glass, forming fog—especially on rainy or humid days. Dealing with it is actually simple: I adjust the vents downward to avoid the windows, crack the windows slightly for better airflow, or raise the AC temperature to avoid extreme cold. Newer cars usually have a defogging function that handles it with a single button, while older models require a bit more manual effort. Remember to pull over safely if fogging occurs instead of forcing your way through—wiping the glass is a safer bet. Developing good habits, like using the external air circulation mode when starting the car, can help reduce this annoying issue.
As someone who loves studying cars, I'm quite clear about the principle of fogging caused by air conditioning: in summer, turning on the cold air reduces the temperature and humidity inside the car, but the glass remains hot due to external heat, causing condensation into fog when the temperature difference drops below the dew point. This phenomenon is more pronounced in hot and humid weather, essentially a thermodynamic occurrence. I often recommend using the mixed-mode air conditioning or activating the defogging system to balance temperature and humidity; upgrading the air filter or using automatic climate control can effectively reduce the frequency of fogging. Safe driving is the priority—when fogging occurs and visibility is compromised, it's crucial to slow down and address it promptly.
