What is the difference between internal and external air circulation in a car?
2 Answers
The difference between internal and external air circulation lies in the way air is circulated: internal circulation draws air from inside the vehicle, primarily to prevent dust from entering the cabin; external circulation draws air from outside the vehicle, which is then cooled or heated by the air conditioning system before being blown out through the vents, thereby replenishing fresh air and improving the air quality inside the car. Internal circulation helps maintain temperature; when the internal circulation button is activated, the airflow channel between the inside and outside of the car is closed, mainly to prevent external dust from entering the cabin, reduce the intake of harmful gases, and effectively block harmful exhaust emissions from vehicles ahead. External circulation uses a fan to draw outside air into the car, maintaining air circulation and promptly replenishing fresh air inside the cabin. When driving on highways, keeping external circulation on allows harmful gases inside the car to dissipate more quickly.
I noticed many people are unclear about the difference between a car's recirculation mode and fresh air mode. Simply put, recirculation mode circulates only the existing air inside the vehicle without drawing in outside air, while fresh air mode introduces fresh air from outside. I switch between them based on conditions while driving: when there's heavy pollution outside, like during traffic jams or smoggy days, I use recirculation to avoid inhaling dust or odors. It also saves a bit of fuel since the AC doesn't need to adjust extra hot air from outside. However, prolonged use of recirculation can make the cabin stuffy and cause dizziness, so I only use it briefly when necessary. Fresh air mode is ideal during good weather or when first entering the car for ventilation. It helps defog windows, especially on rainy days when condensation forms. For daily use, alternating between both modes maintains cabin comfort and health, preventing fatigue caused by poor air quality.
