Which air circulation mode should be used when car windows fog up in rainy weather?
3 Answers
When car windows fog up during rainy driving, the external air circulation mode should be activated. External circulation uses a fan to draw outside air into the vehicle cabin. Even when the fan is off, moving vehicles naturally draw in airflow to replenish fresh air inside. Internal circulation closes the airflow passage between inside and outside, creating an internal air recirculation system that effectively blocks external dust and harmful gases while maintaining cabin temperature. Automotive air conditioning systems serve three main functions: 1) Cooling, heating, ventilating and purifying cabin air; 2) Providing passengers with a comfortable environment; 3) Reducing driver fatigue and improving driving safety.
I have quite some experience with foggy car windows on rainy days. The best approach is to turn on the external air circulation mode, as it draws in fresh, dry air from outside, reducing humidity inside the car and helping the fog dissipate more easily. I remember one time during heavy rain when there were several people in the car—the humidity rose quickly, and the windows fogged up so fast I could barely see the road. Luckily, I switched to external circulation in time, and within minutes, the windows cleared up significantly. If you use internal circulation instead, the moisture inside just keeps recirculating, making the problem worse. Keeping a cloth handy to wipe the windows helps, but the real solution is adjusting the air conditioning system properly. For cars with automatic AC, simply press the external circulation button and set the temperature slightly lower for faster results. This way, you can drive with much more peace of mind, avoiding the danger of blurred vision.
Driving in the rain with foggy windows is no trivial matter—safety comes first. Personally, I recommend turning on the external air circulation first, as it draws in outside air to quickly reduce humidity inside the car and prevent fogging. As someone who frequently travels with family, I always say: don’t panic or slam on the brakes when fog appears. Switch the AC to defrost mode and activate external circulation—the fog will clear faster, and driving will feel more stable. Avoid using internal circulation on rainy days, as it recirculates exhaled moisture, making fogging worse. If all else fails, crack the window for a few seconds to ventilate, but don’t leave it open too long to avoid rain getting in. Make it a habit to check your AC settings proactively—don’t wait until visibility is compromised to regret it.
