In winter rainy days, should the defogging use internal or external air circulation?

[VanEvelyn]

In winter, when using warm air for defogging, you can first adjust the air circulation mode to external circulation to reduce the temperature difference between the inside and outside of the car. After waiting for a few minutes, switch to internal circulation mode. Using anti-fog spray: When using defogging spray, car owners only need to spray it evenly on the glass surface and then wipe it clean with a dry towel. After wiping, a protective film will remain on the glass surface, altering the surface tension of water molecules and causing fog droplets to coalesce into larger water droplets, thus not obstructing the view. This method is also applicable to other car glass surfaces, especially the exterior rearview mirrors. Homemade defogging spray with dish soap: Mix dish soap with water in a 1:6 ratio, put it in a bottle, and spray and wipe it before traveling. The effect is comparable to commercially available defogging sprays, though the durability is slightly inferior.

[LaEmiliano]

Last winter when I was driving home in the rain, my car windows suddenly fogged up completely, making it almost impossible to see the road. After thinking about this issue, I realized that defogging requires using the external air circulation. Because humidity inside the car is high on rainy days, human breathing causes fogging. External circulation brings in dry air from outside to remove the moisture inside. If you use internal circulation, you're just recirculating the humid air inside, which will make the fog worse. My usual method is to first turn on external circulation, then press the defog button with the fan at maximum speed blowing on the front windshield - the fog clears in about two to three minutes. Setting the temperature to around 23 degrees is most comfortable - if it's too hot, the temperature difference between inside and outside the glass can actually cause new fog to form. Opening the windows slightly while defogging helps with ventilation too, even though it's a bit colder - safety comes first after all.

[ErinDella]

Yesterday when I was driving my child to school in winter rain with fogged-up windows, I quickly switched the AC to external circulation. You really shouldn't use internal circulation - it traps the moisture from passengers' breath inside, and when cold rain hits the windows, they instantly fog up completely. After switching to external circulation, I immediately noticed the air becoming drier and the defogging worked much faster. I also made sure to adjust the air vents to blow directly at the windshield with the heater at maximum to help evaporate the moisture. If the fogging is particularly heavy, keep the AC temperature moderate - not too hot or too cold, 21°C is ideal. Oh, and regularly changing the cabin air filter is crucial too - a dirty filter makes the air more humid. These small details really matter for driving safety and shouldn't be overlooked.

[VanDawson]

As an experienced driver, I recommend using the external circulation mode for defogging in rainy weather. Internal circulation only recirculates the air inside the car, which in winter rain conditions will make the fog on the windows increasingly thicker. External circulation directly introduces outside air with lower humidity, making defogging easier. The operation is simple: press the defog button, and the system will automatically switch to external circulation mode. Then set the temperature around 22 degrees Celsius, adjust the fan speed to medium-high, and direct the airflow toward the windshield. Avoid using internal circulation and cold air, as cold air can cause frost to form on the outside of the glass, creating more trouble. Keep the temperature difference between inside and outside the car within 8 degrees for quick and safe defogging.

[MacZane]

Fogging up in the car during winter rain is very dangerous, and I've specifically researched this issue. The key is to select the external air circulation mode, which introduces drier outside air with about 15% lower humidity than inside the car, making defogging more efficient. When I encounter fogging, I immediately switch to external air circulation mode while activating the defogging function, directing warm air specifically at the windshield. Maintaining a temperature around 22 degrees Celsius is most reasonable, as both high heat and cold air can easily cause new fog formation. A special reminder: avoid using internal air circulation, as it essentially recycles moist air. Make it a habit to check the air circulation mode every time you start the car and keep the air filter clean - these small practices can significantly reduce the likelihood of fogging.