Should You Use Hot or Cold Air to Defrost the Windshield on Rainy Days?
3 Answers
Using cold air to defog the windshield on rainy days is generally faster. When cold air is blown onto the glass, the fog quickly dissipates, providing a rapid and direct effect. This happens because the cold air creates a "cold air film" on the glass surface, preventing carbon dioxide from condensing on the glass and thus achieving the defogging effect. Below are some methods for defogging car windows: 1. Apply Anti-Fog Spray: Spray a small amount of defogging agent onto the car window and wipe it clean. This removes dirt and stains while forming a thin, transparent protective film on the glass, effectively preventing moisture from condensing and forming fog. 2. Air Conditioning Cooling: Use the air conditioning's cooling and dehumidifying function to reduce air humidity and remove fog. In summer, especially when many people enter the car without turning on the air conditioning promptly, the exhaled humid air can quickly cause the windshield to fog up. In this case, turn on the air conditioning and direct cold air toward the windshield. The dehumidifying function will quickly remove the fog.
Frost on the windshield during rainy days is a common issue, and I prefer using warm air to address it. Warm air quickly heats the glass surface, reducing the temperature difference between the inside and outside, making it harder for moisture to condense. Additionally, turning on the air conditioning compressor for dehumidification speeds up the dissipation of fog. Using cold air, on the other hand, may cool the glass further, worsening condensation, especially when the interior humidity is high during rainy days. It is recommended to switch to defrost mode after starting the car, direct the airflow toward the windshield, set the fan to medium or high speed, and use the recirculation mode to minimize external moisture from entering. Cleaning the interior glass is also crucial to prevent residual dirt from attracting moisture. As part of my daily driving routine, I warm up the car for a few minutes before operating these settings to ensure system efficiency. Safety comes first—promptly removing frost prevents obscured driving vision, especially on slippery roads.
I've driven various cars and always use hot air to deal with windshield fogging in rainy weather. Hot air heats and dries the air, providing immediate results, unlike cold air which may worsen condensation. On rainy days, I directly press the defrost button (if available), turn on the air conditioning for dehumidification, and adjust the temperature knob to the warm zone. Remember not to rush to open windows or blow cold air, as that introduces more moisture and can backfire. Using a microfiber cloth along with hot air speeds up the process, and regularly cleaning the inside of the windshield helps prevent fogging. It's simple and effective—I never use cold air for defrosting as it's only suitable for extreme heat to cool down. Developing a habit of checking interior humidity, like drying seats promptly after rain, can reduce the frequency of fogging.
