Should the AC be turned on for defogging?

[SanLola]

Generally speaking, when using cold air for defogging, the AC should be turned on, while when using warm air for defogging, the AC does not need to be turned on. If the local air is relatively dry, you can also choose not to turn on the AC and instead crack open the car windows to allow air circulation inside the car, reducing the temperature difference between the inside and outside of the car. However, this method can be quite cold in winter. The correct methods for car defogging: 1. In summer: You can turn on the car's defogging mode, set the fan speed to maximum, then turn on the AC and lower the temperature. The fog on the windows will disappear shortly. 2. In winter: You can turn on the warm air, the front windshield defogging function, and the AC. Although warm air defogging is not as fast as cold air, and the fog on the windows may worsen initially when warm air is first turned on, this method provides better defogging results. It prevents 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.

[EmmaLynn]

When I encounter foggy windows while driving, I immediately turn on the AC. Once the compressor kicks in, the dehumidifying effect is instant. Especially on rainy days or when there are many passengers in the car during winter, the windshield clears up in just a few seconds. Although using the AC consumes a bit more fuel, safety comes first. Remember to adjust the air vents to the windshield mode and turn on the external circulation for better ventilation. Once, I tried to save fuel by only using the heater, but the fog got thicker and thicker, almost causing a rear-end collision. That scared me so much that I never dare to turn off the AC for defogging again.

[VanElliot]

As an auto mechanic, I've encountered numerous vehicles involved in accidents due to fogging. I sincerely recommend everyone to use the AC for defogging. Car air conditioning isn't just for cooling; its core function is dehumidification! When humid air comes into contact with cold glass, it's the same principle as water droplets forming on an iced beverage bottle. Turning on the AC allows air to pass through the dry evaporator, reducing humidity and preventing fogging. Although using the AC in winter may make the airflow slightly cooler, combining it with the heater is actually more efficient. Some car owners worry about compressor wear, but typically, defogging only takes a few minutes, which has negligible impact on the machine.

[IsabelleMarie]

Last week when teaching my wife to drive, I realized many people don't even understand the logic of automatic climate control. When pressing the windshield defogger button, most vehicle models will automatically activate the AC light - the system itself engages the compressor for dehumidification. Manually turning off AC actually interferes with the programmed control. New energy vehicles are even smarter now - like Tesla's defog mode which intelligently starts/stops the compressor based on interior/exterior temperature and humidity readings. But for older cars, note: if the AC button isn't lit, manually turn it on, otherwise just blowing air is very inefficient.

[McNathan]

Using AC for defogging essentially replaces moist air with dry air. I conducted an experiment for comparison: two cups of boiling water were placed in the car, and after 30 minutes of blowing hot air with the AC off, the fog remained; with the AC on and external circulation, the fog cleared in just 3 minutes. A detail often overlooked: do not use internal circulation when defogging! The moisture exhaled by passengers will accumulate in circulation. It's best to prevent fogging in advance during the rainy season by applying anti-fog spray on the glass—available on Taobao for ten yuan a bottle, lasting half a year. If fog suddenly appears, don't panic; immediately turn on the AC and blow the maximum airflow at the glass, which is a hundred times safer than wiping with a cloth.

[RyleeLee]

During the southern rainy season, I use the AC to defog my car every day. The compressor's dehumidification is much more thorough than relying solely on the heater's physical moisture removal. The cold air can quickly cool the glass, lowering the dew point. Nowadays, hybrid cars have an additional hidden advantage: utilizing battery waste heat. When I turn on the AC to defog in my Li L9, the system prioritizes the electric-driven compressor, and the engine doesn't even need to start. For traditional car owners concerned about fuel consumption, here's a tip: first use the AC for strong defogging, then turn it off once visibility is clear and switch to the heater to maintain temperature. If fogging recurs, simply repeat the process.