What do the car's internal and external circulation mean?

[MiguelLee]

Air is circulated internally by the blower moving the air inside the car, while external circulation involves airflow entering the blower through wind pressure or air ducts. The two circulation modes are used as follows: 1. External circulation usage: (1) After purchasing a new car, turn on the external circulation to allow harmful gases inside the car to volatilize and dissipate. (2) When driving on the highway for extended periods, turn on the external circulation to replenish oxygen inside the car. 2. Internal circulation usage: (1) During traffic jams when exhaust fumes are dense, turn on the internal circulation to prevent outside exhaust from entering the car. (2) In sandy or dusty weather, turn on the internal circulation to prevent outside dust from entering and reduce the impact of sand on the air filter.