Which consumes more fuel, the car's internal circulation or external circulation?

[VanAdrian]

Using internal circulation is more fuel-efficient than external circulation, but in practical use, the difference is negligible. Relevant explanations are as follows: 1. When external circulation is on, the hot air drawn from outside the car is cooled by the air conditioning evaporator before entering the car. The temperature of the outside hot air remains relatively constant before passing through the evaporator and does not change with the duration of air conditioning use. Therefore, this cooling process is relatively slow, requiring a longer time to reduce the car's interior temperature to the set value. 2. When internal circulation is on, the fan directly draws air from inside the car, which is cooled by the air conditioning evaporator and then blown out through the vents. As the interior temperature decreases, the temperature of the air drawn by the fan also gradually lowers. With a constant air conditioning cooling capacity, the temperature of the cooled air blown out from the vents will be lower, creating a positive feedback loop that quickly reduces the car's interior temperature to the set value.