Should You Use Cold or Hot Air to Defog the Car in Summer?
4 Answers
Whether to use cold or hot air to defog the car in summer depends on the specific situation. Here is a detailed explanation: 1. Cold air defogging: The root cause of window fogging is the significant temperature difference between the inside and outside of the car—cold outside and warm inside, leading to window fogging. 2. Hot air defogging: When using hot air to defog, the fog on the car windows may initially become heavier, but after a while, the hot air will dry it out. 3. Opening windows or using defogging spray: You can open the car's sunroof (or windows) while driving to maintain the same temperature inside and outside the car, preventing fogging.
In summer, I highly recommend using the air conditioning to defog the windshield. Fogging occurs due to temperature differences between the inside and outside of the car, causing moisture to condense on the glass. Using cold air defogs faster. I usually turn on the AC, lower the temperature, and direct the cold air toward the windshield, which quickly reduces humidity inside the car. Remember to switch to the fresh air mode (external circulation) to bring in dry air from outside—this typically clears the fog within 30 seconds. If you use recirculation mode (internal circulation), the fog might worsen because the moisture from passengers' breath keeps circulating. Of course, if it gets too cold after prolonged use, you can adjust the temperature back to a comfortable level—by then, the fog usually doesn’t reappear.
Using cold air for defogging in summer shows immediate results. After starting the car, I immediately turn on the AC and switch to MAX mode, setting the airflow to blow directly onto the windshield. The cold air quickly lowers the glass temperature, making it difficult for water droplets to adhere. Once during heavy rain while picking up my child from school, the windshield fogged up completely as soon as I got in the car. Turning on the cold air + external circulation cleared my vision in just 20 seconds. If you use hot air instead, the insufficient engine coolant temperature at startup can actually worsen the fog initially. However, prolonged use of cold air requires caution to avoid directing the vents at people—a friend of mine developed frozen shoulder from prolonged exposure to direct cold airflow.
In summer, prioritize using the cold air for defogging. When you first get into a car that has been baking in the sun, the windows tend to fog up because hot air meets the cold glass. Turning on the AC with the recirculation mode off solves the problem the fastest. Remember to lower the AC temperature and direct the airflow toward the windows—the fog should clear up in about half a minute. Using hot air isn’t effective right after starting the engine; you’ll need to wait for the coolant to warm up. Once, I tried using hot air to defog, and for the first five minutes, the fog got worse—I almost missed the highway toll booth. After using cold air to dehumidify, remember to switch back to a normal temperature to avoid catching a cold.
