What is the purpose of the external air circulation in a car?

[SavannahAnn]

Here is a related introduction about the internal and external air circulation in cars: 1. The working principle of external circulation is to use a fan to bring outside air into the car and expel the air inside the car through the fan, achieving the effect of air exchange without opening the windows. 2. The principle of internal circulation is to allow the air inside the car to circulate, especially when using the heater in winter or the air conditioner in summer to promote air circulation inside the car. The air conditioner in summer works by using the compressor, so it is necessary to turn on the AC button and then activate the air conditioner, which results in higher fuel consumption when using the air conditioner in summer. 3. When the air conditioner is turned on, if the temperature inside the car is higher than the outside temperature, the front windshield will fog up. At this time, the external circulation must be turned on to achieve a defogging effect. In winter, the car's heater operates using the heat generated by the engine during operation, and the engine's cooling is managed by the radiator.

[TannerFitz]

For me, the car's fresh air mode is a great way to refresh the air inside the vehicle. Instead of recirculating the same cabin air, it directly draws in fresh outside air. During my daily commute, especially in traffic jams with windows closed, the stuffy air makes me drowsy. Turning on fresh air mode noticeably improves breathing comfort and alertness. This mode is also useful on rainy days as it prevents window fogging that could impair visibility. However, on heavily polluted or smoggy roads, I'm careful not to use fresh air mode for too long to avoid inhaling poor-quality air. Overall, making a habit of using fresh air mode helps maintain a cleaner, healthier cabin environment and reduces fatigue driving risks – it's quite practical.