What do the internal and external air circulation modes in a car mean?

[LeJuniper]

External circulation refers to the airflow between the outside and inside of the vehicle. The air blown by the fan comes from outside the car, and even when the fan is not turned on, air is still drawn into the car while driving, replenishing the fresh air inside. Internal circulation closes the airflow passage between the inside and outside of the car. Without the fan, there is no airflow circulation. When the fan is turned on, the air drawn in comes only from inside the car, creating an internal airflow cycle. Here is more information about internal and external circulation: 1. External circulation principle: When external circulation is activated, the car's fan draws air from outside into the car, allowing air from outside and inside the car to circulate. Even if the fan is not turned on, air will still enter the car while driving, providing fresh air from outside. 2. Internal circulation principle: When internal circulation is activated, it means the airflow passage between the inside and outside of the car is closed. Without the fan running, there is no airflow circulation inside the car. When the fan is operating, the air drawn in comes only from inside the car, ensuring that the airflow inside the car continues to circulate.