What is the Difference Between the External and Internal Circulation of a Car's Air Conditioning System?

[Cheryl]

The difference between the internal and external circulation modes of a car's air conditioning system is significant. The most obvious distinction lies in their respective indicator symbols, followed by their functional differences. Internal circulation recirculates the air inside the vehicle cabin, which allows for faster temperature adjustment but may reduce air quality over time. External circulation draws fresh air from outside the vehicle. It's advisable to switch to internal circulation when encountering poor outdoor air quality, dusty road conditions, or when following diesel vehicles emitting substantial exhaust fumes. Below are the primary functions of car air conditioning systems: 1. Temperature Regulation: This is the core function. In summer, the cooling system lowers cabin temperature, while in winter (except for large commercial vehicles that use independent combustion heaters), most vehicles utilize residual engine heat for warmth. 2. Humidity Control: Humidity significantly impacts passenger comfort. Ideal cabin humidity should be maintained between 30%-70%. Standard car AC systems don't actively regulate humidity - this requires ventilation systems or the advanced integrated climate control systems found in luxury vehicles. 3. Airflow Adjustment: Both airflow velocity and direction crucially affect comfort. When air is directed at passengers, velocity should be carefully regulated according to individual preferences, considering factors like age, health conditions, and thermal preferences. 4. Air Purification: Maintaining cabin air quality is essential for passenger comfort.