Should AC Be Turned On for Defogging?
4 Answers
Defogging does not require turning on the AC. Additional information about AC is as follows: 1. The AC button is used to activate the air conditioning's cooling function, while defogging requires heating. 2. The AC button controls the air conditioning compressor, which is used for cooling; whereas the warm air function utilizes the car's internal heat circulation and does not require activating the air conditioning compressor. Therefore, to use warm air, you only need to adjust the air conditioning settings without turning on the AC. Additional tips: To defog, start the car, turn on the warm air conditioning, and set the air circulation to external to expel the cold air from the car. After 2 to 3 minutes, switch the air circulation back to internal.
Our car gets extremely foggy on rainy days, and I always turn on the AC along with the defrost button. Once the AC is on, the compressor kicks in and removes the moisture inside the car, quickly clearing the fog on the windows. You might think the AC is only needed in summer, but it’s even more essential in winter when fogging occurs! Even if you’re using the heater, don’t turn off the AC, or the windshield will get blurry again. Once, when picking up my kid from school during a heavy downpour, I couldn’t see the rearview mirror at all without the AC—the condensation made it look like frosted glass. Now I’ve made it a habit: as soon as I turn the knob to the defrost setting, the AC light automatically turns on, which is super convenient. If the fog is heavy, cracking open the fresh air vent helps with ventilation, but don’t turn off the AC—that’s the key to dehumidifying!
The most annoying thing about driving in winter is the fogging up of car windows, especially when there are many people in the car. Based on my experience, using the AC to defog is the fastest method—just make sure the little snowflake icon lights up when you press the defrost button. The principle is simple: when the AC is turned on, the evaporator temperature drops, causing the moisture in the air to condense into water droplets and be drained away, resulting in dry air being blown out. Have you ever tried using just the heater to defog? It takes three to five minutes for the warm air to dry the glass, while cold air defogging clears the view in just 15 seconds. However, I recommend setting the temperature a bit higher—this way, it removes humidity without making you shiver from the cold. A while ago, on the way to skiing, my friend was shivering from the cold and wanted to turn off the AC, but as soon as it was turned off, the fog quickly returned, so we quickly turned it back on.
A seasoned driver once taught me a trick: the AC acts like a car's dehumidifier. Although it consumes a bit more fuel, safety comes first! Especially during the southern rainy season, fogging on the windshield is even more dangerous than dim lights. Yesterday, driving back home on mountain roads, I encountered thick fog—seeing the AC light on the dashboard put me at ease. The compressor removes the moisture, and the hot air dries the glass, working together to clear the fog quickly. A reminder to new drivers: don’t be fooled by AC equaling cold air. Modern cars are smart—when you set the temperature to 28°C, the AC blows hot air. Wipers can clear water but not fog; you still need the AC! Sudden fog on the highway is terrifying—don’t wait for the heater to slowly dry it; AC defogging is a lifesaver!
