Should the Car Air Conditioner Use Internal or External Circulation?

[MacBrooke]

Whether to use internal or external circulation in a car's air conditioning system depends on the situation. Generally, when turning on the air conditioner for cooling or heating, you can first activate the internal circulation to quickly lower or raise the temperature inside the car. Once the temperature stabilizes, it's advisable to switch to external circulation to allow fresh air from outside to enter. Below are the details: Internal and External Circulation: The air intake for internal circulation is inside the car, meaning outside air cannot enter, and inside air cannot exit. The air intake for external circulation is located below the front windshield wiper, at the junction of the windshield and the engine hood, drawing in outside air. The Difference: The most noticeable difference is in air freshness. With prolonged use, internal circulation can lead to stale air, reduced oxygen levels, causing discomfort, fatigue, anxiety, and affecting driving safety. External circulation ensures airflow between the inside and outside of the car, preventing excessive carbon dioxide concentration.