What is the difference between the car's internal circulation and external circulation?

[LaDerek]

Internal circulation means that the air inside the car circulates when the car is closed. The icon is a closed car interior with a circulating arrow; while external circulation means that the air outside the car flows into the car. The icon is an unclosed car with an external air arrow pointing into the car. The specific differences are as follows: 1. Internal circulation refers to the air inside the car being heated or cooled before being sent back into the car; external circulation refers to the air outside the car being heated or cooled before being sent into the car, which means gas exchange between the inside and outside of the car. 2. Generally, when we turn on the air conditioning for cooling or heating, we can first turn on the internal circulation to quickly lower or raise the temperature inside the car; when the temperature stabilizes, we can appropriately switch to external circulation to exchange air with the outside. If the air quality outside the car is not good, such as in traffic jams with a lot of exhaust fumes or in underground parking lots, do not turn on the external circulation. If you are driving on the highway, do not open the car windows, just turn on the external circulation. When the air outside is good and you feel stuffy inside the car, quickly turn on the external circulation for air exchange; if you want to maintain the air inside the car, turn on the internal circulation.

[CarsonFitz]

As a seasoned driver with years of experience, I've personally experienced the difference between recirculation and fresh air modes. Recirculation keeps the air inside the car circulating, like when using AC on hot days—it cools faster and saves fuel by not drawing in outside air. Fresh air mode brings in outside air, which is useful for ventilation, such as defogging windows on rainy days or eliminating odors inside the car. The key difference is: recirculation maintains cabin temperature more efficiently, especially in traffic to avoid exhaust fumes, while fresh air mode ensures better air quality but reduces AC efficiency. I often alternate between them on long drives to prevent stuffiness and driver fatigue. A helpful tip: use recirculation for quick cooling after restarting in summer, and start with fresh air mode in winter to dehumidify before switching to heat—these habits enhance comfort, safety, and extend your AC system's lifespan.

[VanIsla]

From an air flow dynamics perspective, this is quite fascinating. In recirculation mode, the AC system only cycles interior cabin air without drawing external airflow through the fan, enabling rapid temperature adjustment. Exterior circulation opens the air intake flap to introduce outside air—while providing fresh oxygen, it also brings in dust/pollutants. The key distinction: recirculation better maintains stability (e.g., blocking pollen/exhaust), whereas exterior circulation promotes air exchange to reduce window fogging. Practically, I often use recirculation in heavy traffic to minimize pollutant intake, then switch to exterior mode on highways. Note: overusing recirculation may cause stuffy humidity—recommend alternating modes hourly for optimal comfort.

[Smith]

From a safety perspective, the difference between recirculation and fresh air modes is significant. Recirculation uses the air inside the vehicle, which helps maintain stable temperatures but may result in less fresh air; fresh air mode introduces outside air, providing oxygen to improve air quality and especially preventing window fogging. The key is to switch flexibly while driving: use recirculation in traffic jams or tunnels to prevent pollution, and fresh air mode on rainy days or during long drives for ventilation. Personal experience tells me that intelligent use of these modes can enhance driving safety, avoiding fatigue and accidents.