What is the difference between the internal and external circulation of a car's air conditioning system?
2 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.
