Should You Use Internal or External Air Circulation for Defogging in Rainy Weather?
3 Answers
For defogging in rainy weather, use the external air circulation. If the rain is not too heavy, you can also slightly open the windows for quicker defogging. Car air conditioning systems have both internal and external air circulation modes, but many drivers do not use them correctly. If you are driving on long-distance or highway routes where opening windows for ventilation is inconvenient, it is recommended to use external air circulation. If you are driving in congested urban traffic, it is advisable to switch to internal air circulation. Car air conditioning systems are equipped with air filters, which need to be replaced regularly. Generally, it is recommended to replace the air filter every 10,000 kilometers. The air filter is designed to purify the air. If it is not replaced for a long time, it can affect the performance of the car's air conditioning system and the health of the passengers.
On rainy days when the windows fog up, I usually turn on the external air circulation to defog. This is because the external circulation draws in dry air from outside, helping to expel the moisture inside the car; pressing the AC button at the same time enhances the dehumidification effect. If you use internal circulation, it only recirculates the moist air inside, and the accumulated humidity can make the fog worse, impairing visibility and creating danger. Having driven for many years, I use this trick whenever it rains: turn on the windshield defrost mode, set the temperature to around 20 degrees, and keep the external circulation running continuously. Occasionally, if the fog is very heavy, I first use internal circulation with hot air for dehumidification for about 10 seconds, then immediately switch back to external circulation to maintain fog prevention. Don’t forget to check if the cabin air filter is dirty—regular cleaning can improve defogging efficiency. This method is safe and reliable, reducing the risk of accidents and making rainy-day driving more reassuring.
As an average driver, I rely on the external air circulation to defog my car on rainy days. The external circulation draws in relatively dry outside air, which, combined with the air conditioning's dehumidifying function, effectively clears fog. Using the internal circulation, on the other hand, traps moisture inside the car, worsening the fogging. Initially, I didn't know better and used the internal circulation, resulting in a white, hazy windshield that was hard to see through. Later, I learned the correct method: turn on the AC, select the windshield vent, and increase the fan speed. If there are passengers exhaling a lot of moisture inside the car, the external circulation helps disperse the humidity faster. Remember, you can also pre-ventilate the car by turning on the external circulation before parking, avoiding panic during the drive. Keeping the windshield clear is crucial for safety, and following these steps makes driving much smoother every time.
