How to Use the Car's Internal and External Air Circulation?

[AriannaDella]

Internal circulation prevents outside air from entering the car, aiming to block harmful particles from coming in with fresh air. On the other hand, external circulation can slightly improve fuel efficiency when used in winter. The specific operations for internal and external circulation are as follows: 1. The purpose of external circulation is to replenish fresh air inside the vehicle, while internal circulation keeps dirty air out. External circulation introduces outside air into the car, whereas internal circulation only recirculates air from within the vehicle, creating an air cycle inside the cabin. When entering a car in summer where the interior temperature is high, turn on the air conditioning, select A/C cooling, and then switch to external circulation. Since the interior temperature is higher than outside, external circulation helps cool the car faster by quickly replacing the hot air inside. Once the temperature drops, switch back to internal circulation to retain the cool air, ensuring better cooling and insulation. 2. Internal and external circulation should not be used rigidly—keeping one mode constantly can affect health. Adjust according to actual conditions. For example, in hot weather, a car parked outdoors temporarily will be too hot to sit in directly. Open the windows and turn on external circulation to let the hot air escape. Then close the windows, turn on the air conditioning, and switch to internal circulation while driving to maintain airflow. In cold weather, start with internal circulation to retain warmth, then switch to external circulation when appropriate. On highways, using external circulation allows air to flow in and out smoothly, improving fuel efficiency. On rainy days, external circulation helps remove fog from the windows, ensuring clear visibility. Additionally, for a newly purchased car, use external circulation and open windows to release harmful gases and eliminate odors.

[McVivienne]

When driving long distances, I particularly enjoy studying the air conditioning system, as the usage scenarios for recirculation mode and fresh air mode are completely different. In traffic jams or areas with poor air quality, I use recirculation mode to prevent exhaust fumes from entering the car. On highways or during good weather, I switch to fresh air mode to allow fresh air to circulate inside. On rainy days when windows tend to fog up, I activate fresh air mode along with the defogging function. Another practical tip is to use recirculation mode first when turning on the AC for faster cooling, and use fresh air mode when heating to avoid excessive dryness. Remember to occasionally switch to fresh air mode when using recirculation for extended periods, otherwise it may cause dizziness—I typically switch every half hour.

[SanJuliana]

When commuting by car, I pay the most attention to the air quality inside the vehicle. The recirculation mode is most suitable for congested urban roads, as it blocks exhaust fumes from the car in front, but don't use it for more than half an hour, or the air will become stuffy. Never use the fresh air mode in tunnels or underground parking garages, but it feels particularly comfortable on country roads or when the air quality is good. Here's a cool tip: using the fresh air mode to expel hot air before turning on the AC in summer can cool down the car faster. I'm used to operating based on the environmental indicator light in the car—a red light means recirculation mode, and a green light means fresh air mode, which is especially user-friendly for beginners.

[LeviFitz]

As a seasoned driver, here's the simplest guide: The button with an arrow pointing into the car activates the external air circulation, ideal for ventilation or defogging. The one with an arrow circulating inside the car is for internal air circulation, best used in traffic jams or when using air conditioning for cooling. Remember these two scenarios: use external circulation on highways to prevent drowsiness, and for faster smoke extraction when smoking; switch to internal circulation during smog or prolonged AC use. Simply press the button to operate—older models may have it near the gearshift, while newer ones feature it on the central control screen's AC panel.

[River]

I often teach customers how to adjust the air recirculation when repairing cars. The external circulation is like opening a window but more stable, suitable for rainy days when ventilation is needed but you don't want to open the window; the internal circulation is a closed loop, which provides better cooling effect. The air conditioning system actually has an automatic switching function. When the AUTO button is pressed, the system will automatically select the mode based on the air sensor. A key tip: Do not use the internal circulation for a long time when heating in winter, as it will cause more severe fogging on the windows. It is recommended to set the temperature and let the system make its own judgment, as most cars are equipped with this smart feature.

[SanAmy]

Usage varies between the north and south due to climate differences. In northern winters, avoid turning on the heater immediately after starting the car—first use the external circulation to expel cold air. During southern rainy seasons, start with internal circulation to prevent moisture from entering the vehicle. On highways, it's recommended to use external circulation to maintain fresh air, while switching to internal circulation in traffic jams prevents exhaust fumes. For urban commuting, a good practice is to use automatic air conditioning with internal circulation during rush hours, then switch to external circulation on weekend outings. Additionally, when a new car has a plastic smell, frequently use external circulation for ventilation. After three to five years, during electrical inspections, pay special attention to whether the circulation valve is stuck.