Should You Turn on AC When Defogging?
3 Answers
Generally speaking, you need to turn on the AC when using cold air for defogging, but it's not necessary when using warm air. If the local air is relatively dry, you can also opt to roll down the windows slightly instead of turning on the AC. Leaving a gap in the windows allows air circulation inside the car, reducing the temperature difference between the interior and exterior. However, this method can be quite cold during winter. Correct methods for car defogging: In summer: You can activate the car's defogging mode, set the fan speed to maximum, then turn on the AC and lower the temperature. The white fog on the windows will disappear shortly. In winter: You can turn on the warm air, the windshield defogging function, and the AC. Although warm air defogging is not as fast as cold air, and the white fog on the windows may intensify initially when warm air is turned on, this method provides better defogging results. It helps prevent secondary fogging while driving and keeps the car warm. When using warm air for defogging in winter, it's best to find a place to stop first, wait for the fog on the windows to dissipate, and then continue driving.
Having driven for ten years, I've encountered countless foggy days, and turning on the AC is crucial for defogging. Once the air conditioning is activated, the compressor works to quickly reduce air humidity. At this point, combining it with warm air blowing on the windshield makes the fog formed by the temperature difference between inside and outside disappear within minutes. Relying solely on warm air without the AC can actually worsen fogging, as warm air carries moisture. In the damp and cold rainy days of the south, it's nearly impossible to manage without the AC—driving with a foggy windshield is downright dangerous. My personal habit is to turn on the AC as soon as I start the car, wait for the fog to clear, and then adjust the temperature as needed. This approach is both safe and hassle-free. Additionally, remember to set the air conditioning to external circulation mode, allowing fresh, dry outside air to enter the car for better defogging results.
As someone who prioritizes driving safety, I've specifically studied defogging techniques. Turning on the AC for dehumidification is a crucial step in defogging, as the air conditioning system can quickly convert humid air into dry, cool air. When combined with warm air, it can instantly clear fog. Relying solely on warm air without the AC can eventually defog the windows, but it takes significantly longer, which is particularly dangerous on highways or in low-visibility conditions. Moreover, from my comparisons, using the AC for defogging results in lower humidity inside the car, preventing fog from recurring during long drives. Especially during the rainy season or sudden weather changes, when windows fog up alarmingly fast, directly turning on the AC + defog button is the most reliable method. Developing this habit can truly prevent many driving hazards.
