Use Internal or External Air Circulation in Winter?
3 Answers
In winter, use internal air circulation when warming up the car, and switch to external air circulation after the temperature rises. Here are the functions of internal and external air circulation: 1. Internal air circulation function: It helps maintain warmth in winter and keeps the air conditioning cool in summer. However, prolonged use of internal circulation, while maintaining temperature easily, increases carbon dioxide levels from passengers' exhalation. Therefore, it's advisable to switch to external circulation every hour to refresh the air. 2. External air circulation function: External circulation uses a fan to draw outside air into the car, meaning the air passage between the inside and outside of the car is open. The air blown by the fan comes from outside, and even if the fan is off, airflow is still drawn into the car while driving, replenishing fresh air. Sometimes, you may feel airflow even with the fan off, which is due to the external circulation setting.
I usually switch between recirculation and fresh air modes based on weather and road conditions. When starting the car, I use fresh air mode to let cold air escape. After a few minutes when the engine warms up, I switch to recirculation for warmth. If the windshield fogs up, I must use fresh air mode to dehumidify until the fog clears, then switch back. On highways, I keep fresh air on to prevent drowsiness from oxygen deprivation, while in traffic jams I use recirculation to block exhaust fumes. In northern regions at -20°C, proper use of air circulation modes saved me 5% fuel consumption and prevented window frost. Once forgetting to switch nearly caused a rear-end collision due to sudden fogging – now I've developed a habit of checking the air circulation button at red lights.
Tried commuting for three consecutive days with only the internal air circulation on, and the windows fogged up every day. Later, I figured out a trick: set the heater temperature to around 22°C, turn on the AC button but turn off the cooling (compressor not working), and switch to external air circulation. This method defogs the windows the fastest and saves fuel! Using internal circulation for short commutes is fine, but for long trips, switch to external circulation for 10 minutes every half hour to ventilate. On rainy or snowy days, using external circulation actually prevents the windows from icing up, as it reduces the humidity inside the car. The worst are those old cars with perfume ornaments blocking the vents—they tend to develop odors whether on internal or external circulation.
