What is the difference between the internal circulation and external circulation in a car?
3 Answers
Internal circulation refers to the air inside the car being heated or cooled and then recirculated back into the car, while external circulation refers to drawing air from outside the car, heating or cooling it, and then bringing it into the car, which means exchanging air between the inside and outside of the car. Internal circulation allows the air inside the car to circulate when the car is closed, and the icon typically shows a closed car interior with a circulating arrow. External circulation, on the other hand, brings outside air into the car, and the icon usually shows an open car with an air arrow pointing into the car from the outside. Whether it's heating or cooling, it's best to first turn on internal circulation. Although the temperature inside the car will drop, the carbon dioxide exhaled by passengers will increase. Therefore, it's advisable to switch to external circulation every hour to refresh the air. When turning on the air conditioning for cooling or heating, you can start with internal circulation to quickly lower or raise the temperature inside the car. Once the temperature stabilizes, it's good to switch to external circulation to exchange air with the outside. However, if the outside air quality is poor, such as in heavy traffic with lots of exhaust fumes or in a poorly ventilated underground garage, avoid using external circulation. If you're driving on the highway, do not open the windows—simply turn on external circulation.
The difference between recirculation and fresh air mode in a car mainly lies in the air source. Recirculation means the air inside the car keeps circulating without drawing in outside air, which is suitable when the outside air quality is poor, such as during urban smog or pollen season, as it reduces dust and odors inside the cabin. However, prolonged use may make the air stuffy and increase the risk of motion sickness, especially during long drives. Fresh air mode, on the other hand, draws in outside air, ensuring better ventilation in clean environments or at high speeds, and helps prevent windshield fogging. In winter, I often use fresh air mode because it brings in dry air, aiding quick defogging—especially useful during rain or snow. From a safety perspective, flexible switching is key: prioritize recirculation in polluted areas and switch to fresh air mode in clean environments. Overusing recirculation may lead to higher CO₂ levels, affecting concentration, so avoid keeping it on for convenience. The automatic mode in climate control systems intelligently switches between modes for ease. Developing good habits improves cabin air quality, enhancing both driving mood and health—check the environment before deciding which mode to use.
Having driven for over a decade, I've found that the recirculation and fresh air modes directly impact efficiency and fuel economy. Recirculation only processes the existing air inside the car, eliminating the need to cool hot external air. This allows for quicker cooling in summer when using AC and saves some fuel. The same principle applies to heating in winter by reducing heat loss. Fresh air mode introduces outside air but increases AC workload on hot days, potentially consuming more fuel. Fuel-saving tip: Use recirculation more often in city traffic or dusty conditions; switch to fresh air occasionally during highway driving to ventilate and prevent drowsiness. On routes with clean air, activate fresh air mode to enjoy natural airflow for a more comfortable cabin. Balanced usage reduces AC strain and extends system lifespan. Additionally, monitor your cabin air filter condition – frequent fresh air usage in dusty environments can clog filters faster. Regular replacement or inspection is a hassle-free habit that maintains smooth air circulation inside and outside the vehicle.
