What Do the Car's External and Internal Circulation Modes Mean?
3 Answers
Car's external and internal circulation modes refer to the air flow states inside the vehicle. Internal circulation means the air circulates only within the car, driven by the blower to cycle the interior air. External circulation connects the interior with the outside environment. While driving, airflow automatically enters the car due to wind pressure, and when stationary, outside air can still enter through the air ducts into the blower, then blown into the cabin. External circulation is also known as the "fresh air" mode. Generally, the car's air should be kept in "external circulation" mode to enhance air exchange between the interior and outside, keeping the driver alert and ensuring driving safety. Therefore, some vehicles have this switch designed to default to external circulation. The following situations require switching to internal circulation: When driving in heavily polluted environments, such as black smoke from the vehicle ahead, dusty roads, or surrounding odors. When using air conditioning for cooling, internal circulation should be used to avoid reducing cooling efficiency. When using the air conditioner to defog or defrost the windshield. During winter when using the heater, it should be in internal circulation mode.
The car's external and internal circulation are two modes of the air conditioning system, which I find particularly practical after driving for over a decade. External circulation is like opening a window for the car, drawing in fresh air from outside, especially suitable in places with clean air, such as the countryside or after rain, making breathing inside the car more comfortable. Internal circulation, on the other hand, closes the window and only circulates the air inside the car, ideal for blocking exhaust fumes during traffic jams or for quickly cooling or heating the car with the AC. I usually switch between them flexibly based on the environment: on scorching summer days, I first use external circulation to expel hot air before turning on the AC; in winter, external circulation is needed to introduce dry air for defogging; on highways, I open external circulation every half hour to refresh the air and prevent drowsiness from high carbon dioxide levels. Remember, don't use internal circulation continuously for more than 30 minutes, as poor air quality can easily cause dizziness.
These two modes are actually the air conditioning ventilation strategies, which I've studied while modifying cars. In recirculation mode, the air conditioning damper closes, completely sealing the cabin, allowing air to only circulate and filter within the car. This makes cooling and heating extremely fast and saves fuel, suitable for short trips or hazy days. Fresh air mode opens the front air intake, continuously drawing in external air, which is then filtered and processed by the air conditioning before being blown into the cabin. It's particularly comfortable to use fresh air mode in areas with good air quality, but you should immediately switch to recirculation mode in tunnels or traffic jams to prevent exhaust fumes. Interestingly, many cars come with an automatic switching function that activates recirculation mode when air pollution is detected. However, be careful not to use fresh air mode on rainy days, as the humidity can worsen window fogging.
