Should the car's heating system use internal or external air circulation?

[OBriella]

Whether to use internal or external air circulation for the car's heating system depends on different situations: 1. When driving in congested urban roads, use internal circulation; 2. When driving on highways or long-distance routes, use external circulation to replenish fresh air in the car, which is beneficial to the health of passengers. Internal circulation mode closes the airflow channel between the inside and outside of the car. Without the fan, there is no airflow circulation, and when the fan is on, the inhaled airflow only comes from inside the car, forming an internal airflow circulation. External circulation mode uses the fan to draw air from outside into the car, where the air passage between the outside and inside of the car is open. The air blown by the fan comes from outside the car, and while the car is moving, airflow is drawn into the car to replenish fresh air.