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

[Miller]

The differences between the car's external circulation and internal circulation are: 1. Different circulation methods: External circulation involves heating or cooling the air outside the car before sending it into the car, meaning gas exchange between the inside and outside of the car; Internal circulation refers to the air inside the car being heated or cooled before being sent back into the car. 2. Different symbols: The external circulation icon is an unenclosed car with an air arrow pointing into the car from outside; The internal circulation icon is an enclosed car with a circular arrow inside. The uses of external and internal circulation are: 1. When turning on the air conditioning for cooling or heating, activating internal circulation can quickly lower or raise the temperature inside the car; 2. When the outside air environment is poor, activating internal circulation is recommended.

[Cory]

I've been driving for many years, and the difference between the outside air circulation and recirculation modes is quite significant. The outside air circulation mode draws fresh air from outside the vehicle, similar to opening a sunroof but with a fan effect. It works best during rain or fog, preventing the windows from getting fogged up. The recirculation mode only circulates the air inside the car without drawing from outside. It's safer to use when stuck in traffic with heavy exhaust fumes or when driving at high speeds with strong winds, as it helps avoid inhaling fine dust. Switching between these two modes is very convenient—just press the air conditioning button. Also, remember to regularly clean the air filter to reduce odors.

[VanElaina]

During urban commuting, I've tried alternating between the recirculation and fresh air modes. The fresh air mode is suitable when the air is clean, such as during outings or early morning highway drives. Turning on the AC instantly refreshes the cabin without any stuffiness. The recirculation mode allows the AC to cool faster, making it ideal for summer traffic jams to avoid inhaling exhaust fumes. Using it long-term saves some electricity and is healthier, plus it prevents window fogging that could obstruct vision. Maintaining ventilation mode is also good for breathing.

[VanMatthew]

I understand the difference when taking my kids out. The external circulation introduces outside air for quick defogging; the internal circulation closes the windows to avoid inhaling pollutants, providing peace of mind during smog or near construction sites. Simply put, switching the button protects breathing, and regularly checking the filter ensures durability.