Why does the AC turn on automatically when defogging is activated?

[SanMatteo]

When the defogging function is activated in a car, the air conditioning also turns on simultaneously. This is designed to accelerate the removal of fog by utilizing the principle of the refrigeration evaporator condensing moisture inside the vehicle. Fogging on the front windshield typically occurs during winter or rainy days. Depending on the season, you can choose between hot or cold air: 1. Using cold air: This method is generally suitable for rainy days in summer. The operation is straightforward—simply turn on the cold air, adjust the vents to the front windshield, and activate the external circulation. This approach quickly and effectively eliminates fogging on the front window. 2. Using hot air: Turn on the hot air, select the front windshield as the vent outlet, and turn off the internal circulation. This method addresses the root cause of fogging but takes longer, making it less suitable for use while driving. However, over time, the fog will gradually dissipate, and the interior will become warm and comfortable, making it ideal for cold winter weather.