What is the function of the car's internal air circulation?

[DeAutumn]

The function of the car's internal air circulation is to promptly and effectively prevent external dust and harmful gases from entering the vehicle. For example, when driving through areas with smoke, dust, unpleasant odors, or in heavy traffic, it blocks the harmful exhaust emissions from the vehicle in front. Another function is to maintain warmth. Using the car's external air circulation allows you to breathe fresh air from outside. When driving at high speeds for extended periods, the air inside the car can become stale, making passengers uncomfortable. If you cannot open the windows, you should use the external air circulation to let in some fresh air. In winter, if the warm air feels too hot, you can turn off the fan and switch to external air circulation. This maintains the interior temperature while providing fresh air, making the ride more comfortable.

[DiHazel]

I particularly enjoy using the recirculation function during my driving commute, especially in congested areas. Simply put, recirculation means the AC only circulates the air inside the car instead of drawing fresh air from outside. What are the benefits? Firstly, it blocks exhaust fumes from vehicles ahead during traffic jams, preventing that unpleasant diesel smell from entering the car. In summer, turning on both the AC and recirculation cools the car down remarkably fast—it becomes comfortably cool within minutes, much more efficient than using fresh air mode. The same principle applies in winter with the heater, as there's no need to heat newly incoming cold air. However, it's important not to keep recirculation on continuously. Prolonged use can increase carbon dioxide levels inside the car, so I usually switch to fresh air mode for a few minutes after 20-30 minutes of recirculation. Activating recirculation when driving through dusty areas or on hazy days noticeably enhances the protective effect of the air filtration system.

[DiAlan]

What I appreciate most about the recirculation mode is its ability to maintain air quality inside the car. Whenever I pass through industrial areas or dusty environments, I immediately switch to recirculation, feeling like the smoke and particulate matter outside are effectively blocked by the doors. With the fresh air mode on, I can detect various unpleasant odors—be it gasoline fumes or pesticide smells—but recirculation acts like putting a mask on the car. During winter, when family members with allergic rhinitis are in the car, activating recirculation reduces the chance of pollen entering the cabin, making it feel like a temporary sanctuary. However, it's important to note that when there are multiple passengers, the duration of recirculation should be carefully managed—preferably not exceeding 30 minutes—otherwise, occupants may noticeably feel the air becoming stuffy, leading to fatigue. My usual practice is to set a 25-minute timer on the music player after turning on recirculation, reminding myself to switch modes.

[VonDeclan]

Switching to recirculation mode when using air conditioning can actually help you save fuel, and this is no joke. When the air conditioning is set to recirculation mode, the system only needs to process the air already inside the car, without having to additionally cool the hot air from outside. On a 35°C summer day, using recirculation mode cools the car at least twice as fast, reduces the compressor load, and significantly lowers fuel consumption. I conducted a test: over the same 20-kilometer urban route, using recirculation mode saved 0.7 liters of fuel compared to using fresh air mode the entire time. The same principle applies to heating in winter—not heating the cold outside air is more energy-efficient. However, it's recommended to switch back to fresh air mode once the desired temperature is reached, as the air purifier can accumulate exhaust gases otherwise. Using recirculation mode in traffic not only saves fuel but also helps avoid inhaling exhaust from the car ahead.