What is the difference between the internal and external circulation of a car's air conditioning system?
4 Answers
Car air conditioning internal and external circulation mainly differ in the following aspects: 1. Different states. Internal circulation mode closes the airflow channel between the inside and outside of the vehicle. Without the fan, there is no airflow circulation, and when the fan is on, the inhaled airflow only comes from inside the vehicle, forming an internal airflow circulation. External circulation mode uses the fan to draw air from outside the vehicle into the cabin, allowing air to flow between the outside and inside. The air blown by the fan comes from outside, and even without the fan, airflow is still drawn into the cabin while driving. 2. Different functions. Internal circulation primarily prevents external dust and harmful gases from entering the cabin promptly and effectively, such as when driving through smoke, dust, areas with strong odors, or in heavy traffic, blocking harmful exhaust emissions from vehicles ahead. External circulation allows for breathing fresh air from outside the vehicle.
When driving, I often switch between the recirculation mode and fresh air mode, and their main difference lies in the source of air. In recirculation mode, the air conditioning only circulates the air inside the car continuously, like a sealed box—air is drawn from the cabin and expelled back in without pulling in fresh air from outside. This mode is most practical in summer, for example, when the car is unbearably hot upon entering, I immediately turn on recirculation, and the AC cools down quickly. It works similarly in winter, heating up faster. However, using it for too long isn’t advisable, as it can feel stuffy or cause window fogging. In fresh air mode, the AC draws in new air from outside, continuously replacing the cabin air, keeping the environment fresher. This is especially useful in traffic jams or tunnels, where outside exhaust fumes are present—using recirculation avoids inhaling them. But in rainy or foggy conditions, fresh air mode helps prevent window fogging. I usually prefer fresh air mode on highways or during long drives to ensure airflow and reduce fatigue. Remember, don’t stick to just one mode—flexible switching is key. It can also save a bit of fuel, as the recirculation mode’s motor consumes less energy.
As a frequent driver, I believe the key difference between recirculation and fresh air modes lies in the direction of airflow. Simply put, recirculation keeps air circulating only inside the car without drawing in outside air. It's very convenient to operate—just press a button and the AC focuses on circulating interior air. I often use it in city traffic with many traffic lights to avoid inhaling exhaust fumes or dust from the road, or during sandstorms to keep the cabin clean. However, its drawback is that prolonged use can deteriorate air quality, with increased CO2 levels potentially causing dizziness, especially when carrying rear passengers. Fresh air mode works oppositely, drawing in outside air to continuously replenish oxygen. I use it more often on highways or in suburban areas, finding the air much fresher; it also helps prevent windshield fogging on rainy days. The downside is slightly higher fuel consumption as the AC works harder to condition the incoming fresh air. For optimal use, combining both modes is most cost-effective—for instance, 30 minutes of recirculation followed by 10 minutes of fresh air ventilation strikes a good balance between comfort and safety.
From the perspective of in-car health, I'm discussing the use of recirculation mode and fresh air mode. Recirculation mode keeps the air circulating within the car, which works quickly but doesn't bring in fresh oxygen. When I use it, cooling or heating is faster, but over time the air becomes stuffy and CO2 accumulates, leading to dizziness. Fresh air mode draws air from outside, bringing in fresh oxygen and maintaining a pleasant environment. However, avoid using fresh air mode in polluted areas or during smoggy days to prevent inhaling dirty air. Switch wisely: use fresh air mode in the early morning when there are fewer cars, and switch to recirculation mode during midday traffic jams.
