Should You Use Internal or External Air Circulation for Car Defogging?

[IsaacLynn]

For car defogging, use external air circulation. When fog appears on the windshield, the quickest method is to first adjust the air vents to the front windshield, turn on the cooling function, and with external circulation activated, the fog on the glass can be blown away in about ten seconds at maximum fan speed. When to use internal circulation: When the outside air quality is poor or heavily polluted, such as on dusty roads, in congested traffic, or near chemical plants with foul odors or unpleasant smells; use internal circulation to prevent bad outside air from entering the car. In summer, to quickly lower the interior temperature using the air conditioning, internal circulation can be used. In winter, using internal circulation can keep the car warmer. When to use external circulation: When internal circulation has been used for a long time and opening the windows is inconvenient, periodically switch to external circulation to allow fresh air into the car. When there are many passengers in the car, using external circulation helps maintain fresh air and prevents excessive humidity inside the car, which can cause window fogging. Related information about internal and external circulation: Internal circulation: Air circulates only inside the car without exchanging with outside air. Internal circulation blocks polluted air by closing the airflow channels between the inside and outside of the car, effectively preventing external dust and harmful gases from entering. External circulation: The car's interior air is connected to the outside air, with outside air flowing in through the front air intake and out through the rear exhaust. External circulation replenishes fresh air. However, when driving in congested city traffic, the car may fill with exhaust fumes, which is a result of using external circulation.