Should You Use Hot or Cold Air to Defog Car Windows in Summer?
4 Answers
Both cold and hot air are equally effective in defogging, but using cold air is more comfortable in summer while hot air is preferable in winter. Here's an introduction to the car air conditioning system: 1. Overview: The car air conditioning system is a device that cools, heats, ventilates, and purifies the air inside the vehicle. It provides a comfortable environment for passengers, reduces driver fatigue, and enhances driving safety. 2. Classification by Drive Type: Systems are divided into independent (powered by a dedicated engine to drive the compressor, offering large cooling capacity and stable operation but with higher costs, larger size and weight, mostly used in large and medium-sized buses) and non-independent (the air conditioning compressor is driven by the car engine, with cooling performance significantly affected by the engine's operation, resulting in poorer stability, commonly used in small buses and cars).
In summer, window fogging is mainly caused by the large temperature difference between the inside and outside of the car. Turning on the cold air to blow directly at the windshield is the most effective way to defog, as the cold air quickly absorbs the moisture from the humid air. Remember to turn on the external circulation to speed up the exchange of air inside and outside the car. Once the fog disappears, switch back to internal circulation for better energy efficiency. Veteran drivers' experience tells us not to use hot air to defog in summer, as the car interior is already hot enough. Adding more heat will only increase the burden on the air conditioning and consume more fuel. If necessary, turn the air conditioning temperature knob to the coldest setting and adjust the airflow direction to the windshield. You should be able to see the road clearly within half a minute.
Turning on the AC provides the best defogging effect. Fogging on car windows occurs when warm, humid air condenses into droplets upon contact with cold glass. The air conditioning system cools while dehumidifying, directly reducing interior moisture below the dew point. Last year, I used this method in my dad's old Jeep to solve visibility issues during rainy days. Some worry about discomfort from cold air, but simply adjusting the vent angle upward solves this. While warm air can theoretically dehumidify eventually, blasting hot air during scorching summers feels unbearable and may accelerate new fog formation.
In summer, decisively turn on the air conditioning for cooling, lower the temperature, and increase the fan speed. The core principle is to reduce air temperature and humidity, preventing water vapor from condensing on the glass. Using warm air is theoretically feasible but practically ineffective: it not only increases fuel consumption but also turns the car cabin into a steamer, and most importantly, it works too slowly. I once tried using hot air to defog on a rainy day, and it took five minutes to take effect while making me sweat profusely. A more effective method is to directly push the temperature control button to the blue low-temperature zone after activating the defogging mode.
