Should You Use Internal or External Air Circulation When Turning on the AC on Rainy Days?

[AbigailRose]

When driving on rainy days, you should turn on the external air circulation. Here are some tips for driving in the rain: 1. Driving in the rain: The biggest issue when driving on rainy days is that the windows are usually completely closed, leading to poor air quality inside the car due to lack of air circulation. 2. Turn on the external air circulation: It is necessary to activate the external air circulation to allow more fresh air from outside the vehicle to enter, ensuring better air quality for the driver and passengers. While driving, the humidity inside the car can become quite high, which may cause the windshield to fog up easily.

[SanHeidi]

I usually use the recirculation mode when driving on rainy days. I've found that the fresh air mode brings in outside moisture, which causes the windows to fog up easily and severely obstructs visibility. I remember once on the highway during heavy rain, I had the fresh air mode on and within minutes the windshield was completely fogged up - I nearly rear-ended another car. Since then, I always start with recirculation mode combined with the AC's defog function, which quickly dries out the interior. However, keeping recirculation on continuously can make the cabin stuffy, and the AC can dry out your face, so I switch to fresh air mode every 10-15 minutes for some fresh air. If the car has automatic climate control, it's even more convenient - just press the AUTO button and it will automatically adjust fan speed based on humidity, switching to recirculation for dehumidification when the rain is heavy. In short, safety comes first in rainy conditions - don't let moisture build up on your windows.

[Emmanuel]

As a car enthusiast, I understand that the key to using air conditioning in rainy weather lies in controlling the humidity inside the car. The external circulation mode introduces outside air, which works fine if the external humidity is low. However, during rainy days, the outside air is often humid and cold, and drawing it in can cause condensation and fogging on the windows. The internal circulation mode recirculates the already dried air inside the car, speeding up the dehumidification process. I recommend turning on the external circulation for a few minutes when it starts raining to dry the outside air, then switching to internal circulation to maintain a dry environment, ensuring clear visibility. If fogging occurs accidentally, use the AUTO mode or manually increase the airflow to the windshield for quick defogging. Don't overlook the car's sensors; some vehicles can automatically detect humidity and adjust the circulation mode. Regularly checking the air conditioning filter is also crucial to prevent impurities from clogging and affecting performance.

[StAniyah]

From a safety perspective, I absolutely prefer using the recirculation mode when driving in the rain. It quickly reduces humidity inside the car, significantly lowering the chance of window fogging. Blurred visibility is a common cause of accidents—I once experienced a rainy night with heavy fogging on the windshield, forcing me to pull over and wipe it clean, which was quite troublesome. My advice is to turn on recirculation mode along with the defogger button as soon as you start the car, setting the fan speed higher to clear moist air in just minutes. For long drives, switch to fresh air mode briefly every half hour to prevent CO₂ buildup and dizziness. Avoid the temptation to use fresh air mode for outside air—external humidity is too high on rainy days, posing significant risks.