Should Car Air Conditioning Use Internal or External Circulation in Winter?
5 Answers
In winter, using the internal circulation mode in car air conditioning effectively prevents external dust and harmful gases from entering the vehicle, providing quicker cooling and heating effects. The external circulation mode, on the other hand, introduces fresh air to maintain airflow between the inside and outside of the car, ensuring clean air inside the cabin. The internal circulation control is located below the front dashboard in the driver's compartment, while the external circulation control is situated below the windshield on the passenger side in the engine compartment. Car air conditioning is designed to regulate and control the temperature, humidity, air cleanliness, and airflow within the vehicle cabin to an optimal state, offering passengers a comfortable environment and reducing travel fatigue.
As a seasoned driver from the north, I recommend turning on the recirculation mode for the first 15 minutes in winter to warm up the car quickly. But never keep it on recirculation for too long—once I left it on for an hour straight and the windows fogged up so badly I couldn't even see the traffic lights, which was super dangerous! Now I use a timer to switch to fresh air mode every 30 minutes for 10 minutes of ventilation. Besides preventing fogging, fresh air mode brings in cleaner air, especially when there are multiple passengers. However, during heavy smog days, fresh air mode can let in PM2.5, so I make sure to install a cabin air filter beforehand and stick to recirculation. Remember not to set the temperature too high—22°C is the most comfortable.
When driving in the south during winter, the humidity can be extreme, and using the external air circulation is the way to go. Last week when the temperature dropped, I drove with the internal circulation on, and within less than 10 minutes, the windshield was completely fogged up. It scared me, so I quickly switched to external circulation and pressed the defog button. Although the cold air is chilly, its dryness helps absorb moisture. If you're really afraid of the cold, here's a little trick: turn on the AC! The compressor dehumidifies three times faster than just using the heater. If it's cold when you first get in the car, use internal circulation for 10 minutes to warm up the interior, but don’t exceed 20 minutes. I always keep a defogging spray in my car for emergencies when sudden fogging occurs.
I used to feel drowsy when using the recirculation mode, only to realize later it was due to excessive CO2 levels. Now I always drive with the fresh air intake on—ergonomic studies show fresh air can improve reaction time by 20%. Especially on long trips, external circulation prevents oxygen-deprived dizziness. However, during early morning highway drives with heavy fog, I set the temperature 3°C higher than outside to minimize condensation. Remember to close sunroofs tightly in rain, otherwise external circulation draws in moisture. A common misconception: Can open windows replace external circulation? Actually, open windows create turbulent airflow and increase fuel consumption!
As a fuel-saving enthusiast, real-world tests show that using recirculated air in winter can save 7% fuel. The engine doesn't need to heat fresh cold air, making the heating system much more efficient. However, prolonged use of recirculated air comes at the cost of fogging and odors. My experience suggests: turn on the AC while opening the front defroster vents with airflow directed downward toward the feet. Switch to fresh air mode for 5 minutes every 25 kilometers to ventilate. There's also a pro tip - for vehicles with automatic climate control, pressing the AUTO button enables intelligent switching between air circulation modes. Before parking, turn off the AC and switch to fresh air mode to reduce mildew in the AC system.
