Should Defogging Use Internal or External Air Circulation?
3 Answers
Defogging should use external air circulation. When fog is detected on the windshield, first adjust the air vents to the front windshield, turn on the air conditioning cooling function along with external circulation, and use the maximum fan speed. It typically takes only about ten seconds to quickly blow away the fog on the glass. If driving on long-distance or highway sections where opening windows for ventilation is inconvenient, external circulation should be activated. If driving on congested urban roads, internal circulation should be used. If driving on congested urban roads, internal circulation should be used. All car air conditioning systems are equipped with air filters, which need to be replaced periodically. Generally, car air filters should be replaced every 10,000 kilometers.
As an experienced driver, I always insist on using the external air circulation when defogging. Fogging is usually caused by high temperature and humidity inside the car. Introducing fresh, dry external air through the external circulation can quickly reduce humidity, significantly improving defogging effectiveness. In contrast, internal circulation just recirculates the same air, which can actually increase interior humidity and make fog harder to dissipate, especially during rain, snow, or morning startups. Having driven various car models, I've found that immediately switching to external circulation mode when turning on the AC, with the front windshield vents open, clears visibility within minutes. Safe driving is paramount - fogged-up windows dangerously obstruct vision. I remind novice drivers not to cut corners; address it promptly to prevent accidents. Using warm air assists better in winter, but don't rely solely on cold air in summer either. Remember this little trick to greatly enhance travel safety.
In my health-conscious and daily driving experience, prioritizing the use of external air circulation for defogging is the optimal choice. Fogging on the windows due to moisture inside the car is caused by excessive humidity in the air. External air circulation brings in dry outside air, quickly balancing humidity and making defogging more efficient. Using internal air circulation during defogging has little effect and may instead promote bacterial growth or odors, and prolonged use can affect respiratory comfort. I have tested this multiple times myself—external air circulation defogs faster and improves air quality inside the car, making long drives less fatiguing. In heavily polluted areas, you can check if the cabin air filter is clean while using external air circulation or briefly switch to internal air circulation for adjustment. Overall, this is not just an operational issue but also relates to personal health and the environment. Maintaining good habits makes driving more enjoyable.
