What to Do When the Windshield Fogs Up Before Turning on the AC?

[DelGenevieve]

In cases where the fog is not too heavy, you can appropriately open both side windows to allow air convection, which helps eliminate the temperature difference on both sides of the windshield, making it difficult for fog to form naturally. Blowing cold air is a quick but temporary solution, while blowing hot air can fundamentally solve the problem of windshield fogging. The principle of defogging agents is simple: spraying a layer on the windshield forms an effective protective film, preventing the condensation of water vapor.

[Eleanor]

It's quite annoying when the windshield fogs up while driving in winter, something I've encountered several times, especially on cold and humid days before turning on the AC. The fog mainly forms due to high interior temperature and humidity, which condenses on the cold glass. My solution is to immediately switch the AC to defog mode by turning the mode knob to direct airflow toward the windshield and increasing the fan speed. At the same time, I turn off recirculation and switch to fresh air mode to reduce humidity. If the car's interior is too cold, I slightly increase the temperature to minimize the temperature difference between inside and outside, which helps the fog dissipate quickly. On drier days, I preemptively wipe the inside of the windshield to keep it clean and free of grease, or apply some anti-fog spray—the kind you can buy at the supermarket works fine. For daily driving, I've developed a habit of checking the AC settings before starting the car. In summer, I avoid blasting the cold air right away and gradually adjust the fan speed to reduce fogging. Keeping these tips in mind significantly reduces fogging issues, making driving safer.

[DiBrynlee]

I noticed that the windshield tends to fog up before turning on the air conditioning, especially during the rainy season. In such cases, I usually press the defog button directly—most cars have this feature marked clearly. Once activated, the AC increases airflow toward the windshield, and you can use either cold or warm air depending on the temperature. It’s also important to check the recirculation mode; if the interior air recirculation is on, humidity inside the car rises, leading to fogging. So, I switch to fresh air intake (external circulation) to let dry air in. A quick test is adjusting the air vent knob to direct airflow toward the glass, and the fog usually clears within minutes. For prevention, I regularly clean the inner side of the windshield during car washes to avoid dirt buildup that accelerates fog formation. Keeping moisture-absorbing bags in the car also helps. In emergencies, stay calm and prioritize safety while handling the situation. During routine maintenance, inform the technician to inspect the AC system’s functionality and ensure all vents are unobstructed—this reduces fogging and ensures a more secure drive.

[StLucas]

Dealing with foggy windshields is simple, just adjust the temperature and airflow. If you notice fog before turning on the AC, quickly switch the air conditioning mode to windshield defrosting and increase the fan speed to dissipate heat and remove moisture. Simultaneously, switch to external air circulation to reduce humidity and maintain ventilation inside the car. Regularly wipe the glass with a cloth as a preventive measure, or buy an anti-fog spray to apply. Remember to stay calm and drive steadily.