Should You Use Cold or Warm Air to Defog in Summer?
2 Answers
Both cold and warm air can be used to defog in summer. Here are the relevant explanations: Both cold and warm air from the air conditioning can remove fog inside the car. Using warm air to blow hot air onto the glass can quickly raise the temperature of the front glass, reducing the temperature difference between the inner and outer surfaces of the window, thereby eliminating fog on the windshield. Using cold air to defog is fast and direct, but prolonged use of cold air can make passengers uncomfortable, so it is recommended to use warm air for defogging. On rainy days, you can use cold air to defog by turning on the air conditioning (AC) for cooling, activating the external circulation, and then directing the airflow toward the windshield at maximum speed. The dry cold air will blow onto the windshield, forming a "film of air" on the surface that prevents water vapor from condensing on the glass, thus making the fog disappear.
Once during a summer rainstorm while driving, my windshield fogged up completely white. I immediately switched to the cold air setting + turned on the AC, adjusted the airflow direction to blow onto the windshield. The fog cleared in less than half a minute. Using cold air actually helps the AC remove moisture, whereas warm air can increase the temperature difference between inside and outside, making the fog worse. Now, whenever I encounter foggy conditions on rainy days, I use this method, especially after pressing the defog button—it's even more effective if you turn on the recirculation mode. Remember not to point the front air vents directly at people to avoid catching a cold; angling them slightly toward the windshield is best. This method works slower on the rear windows, so you might need to rely on the rear window heating function for assistance.
