Should You Use Recirculation or Fresh Air Mode for Dehumidifying the Car Interior?

[LaFinley]

Use fresh air mode for dehumidifying the car interior. Recirculation mode: When the outdoor air quality is poor or heavily polluted, such as on dusty roads, in congested traffic, or near chemical plants with unpleasant odors; use recirculation to prevent outside bad air from entering the car; in summer, to quickly cool down the car interior with air conditioning, you can use recirculation mode. Fresh air mode: You can periodically turn on fresh air mode to allow fresh air into the car; when there are many passengers inside, using fresh air mode can maintain air freshness and prevent excessive humidity in the car from causing window fogging.

[DiChristopher]

I've been driving for over a decade and have learned a thing or two about dehumidification. When you first turn on the AC, always use the recirculation mode to quickly reduce humidity inside the car. The principle is that the evaporator condenses water droplets during cooling, and recirculation allows the limited cabin air to be dehumidified repeatedly. Especially on rainy days when outdoor humidity is high, using fresh air mode would let moisture in, making the windshield more prone to fogging. When the humidity gauge drops to around 50%, I switch to fresh air mode for ventilation, otherwise it gets stuffy after sitting for too long. Remember to set the vents to windshield+foot mode for optimal dehumidification. For long-distance driving, switch to fresh air mode every half hour for air exchange – it's safer for driving.

[DelIsabelle]

Last time when I picked up my child from school on a rainy day, the car fogged up badly, and I figured out a good method. Initially, you must use the recirculation mode for dehumidification, so the air conditioning can focus on handling the moisture inside the car. If you directly turn on the fresh air mode, humid air continuously rushes in, and the windows will fog up again immediately. However, if the recirculation mode is used continuously for more than 20 minutes, the rising carbon dioxide concentration can make people feel drowsy. I usually quickly switch to fresh air mode for ventilation when I feel the air getting stuffy, while keeping the AC button on to maintain dehumidification. When taking the baby out, it's also good to prepare an extra dry towel to promptly wipe off the water droplets condensed on the door frames, which helps maintain a comfortable humidity level.

[Roxanne]

To dehumidify the car interior, turn on the recirculation mode as a closed environment allows the AC to remove moisture faster. The principle is that the evaporator absorbs moisture from the air during cooling, and sealing the cabin is more efficient than fighting external humidity. This is especially noticeable on rainy days when using external air circulation can't keep up with the rate of moisture entering. However, prolonged recirculation worsens air quality, so it's recommended to slightly open diagonal windows for ventilation once humidity drops, which is more fuel-efficient than switching directly to external circulation. Remember to clean or replace the AC filter seasonally—a clogged filter can cut dehumidification efficiency by half.

[ORyder]

Fog removal on rainy days is actually quite simple: turn the air conditioning to maximum, adjust the airflow direction to blow onto the windshield, and press the recirculation button. This will clear the fog in about five minutes. Using the external air circulation mode allows moisture to continuously invade, especially during the humid plum rain season in southern regions, where defogging can take half an hour with no effect. However, keeping the recirculation mode on for too long can cause a leather smell. I usually switch back to automatic mode after dehumidification is complete, as the system will automatically balance between internal and external air circulation. When there are passengers in the back seat, be careful not to let cold air blow directly on their heads, as it can easily cause a chill. Regular use of air conditioning cleaner is also important, as dirty ducts can weaken dehumidification performance.