What are the differences between internal and external air circulation in cars?
2 Answers
Vehicle internal and external air circulation differ in the following aspects: 1. Different working principles: Internal circulation refers to the process where air inside the vehicle is heated or cooled before being recirculated back into the cabin; External circulation involves drawing in outside air, heating or cooling it, and then supplying it to the cabin, effectively exchanging air between the interior and exterior of the vehicle. 2. Different usage methods: When initially turning on air conditioning for cooling or heating, it's recommended to first activate internal circulation to rapidly lower or raise the cabin temperature; Once the temperature stabilizes, appropriately switch to external circulation for ventilation with outside air; If the external air quality is poor, such as in heavy traffic with excessive exhaust fumes or in underground parking garages, avoid using external circulation. When driving on highways, never open windows - simply turn on external circulation instead. When outside air quality is good but the cabin feels stuffy, promptly activate external circulation for ventilation.
After driving for so many years, I have a deep understanding of the difference between recirculation and fresh air mode. Recirculation means closing the external vents, with the AC only circulating the existing air inside the car, like shutting all windows and doors tightly in a room. Fresh air mode, on the other hand, opens a small vent to draw in outside air for mixing. When stuck in city traffic with exhaust fumes, I often use recirculation to avoid inhaling pollution, keeping my throat comfortable. But on highways or country roads, I switch to fresh air mode—letting in fresh air prevents stuffiness and clears fog faster because the incoming dry air quickly blows away window condensation. Using recirculation with cool AC in summer saves fuel since it doesn’t process new hot air; the same logic applies to heating in winter, but avoid prolonged use to prevent dizziness. The best strategy is flexible switching—balancing safety and comfort. Remember this, and driving becomes much easier.
