In Summer, Should You Use Internal or External Air Circulation When Fogging Occurs?
3 Answers
In summer, when fogging occurs, you should turn on the external air circulation. There are two methods to defog a car: 1. Roll down the windows: Allow air convection by partially rolling down the windows to let the cold outside air blow into the car, achieving convection between hot and cold air. This reduces the temperature difference inside and outside the car, helping to eliminate frost and fog. If the weather is extremely cold, you can intermittently open and close the windows; 2. Use the air conditioning defogging system: Adjust the "air outlet mode" to "defogging." This mode mainly controls warm air to ventilate towards the windshield and the front windows near the rearview mirrors for both the driver and passenger seats.
I've been driving for decades, and foggy windows in summer are nothing new. In such cases, I always turn on the external air circulation. Since the outside air is relatively dry in summer, the external circulation draws in fresh air from outside, which helps absorb the moisture on the windows and quickly dissipates the fog. If the fog is heavy, I also turn on the air conditioning in cooling mode—cold air accelerates dehumidification, and the fog clears up fast. Remember not to use internal circulation; it recirculates the damp air inside the car, making the fog worse and compromising driving safety. Especially on long drives, I’ve encountered a few foggy situations where visibility was poor, and relying on external circulation and air conditioning saved the day. For prevention, keeping the glass clean also reduces fog formation, saving you from last-minute scrambling.
When driving my family around, safety is my top priority. In summer, fogged-up windows severely obstruct visibility, so I immediately switch to the exterior air circulation mode. With high external temperatures and low humidity in summer, using exterior circulation allows dry air to enter the vehicle, quickly dispersing the fog and preventing hazardous situations. Combining this with the dehumidifying effect of the air conditioner's cool air yields even better results—typically clearing the fog within minutes. Avoid using interior circulation, as it only increases humidity inside the car. I believe this relates to daily driving experience, and developing good habits in advance is crucial. For instance, in hot and humid regions, I regularly check the air conditioning system to ensure smooth switching between interior and exterior circulation as a precautionary measure.
