Why Can't the Defogger Remove Fog?

[MacAdriel]

Defoggers may fail to remove fog due to temperature differences between the interior and exterior. Here is some information about car defoggers: Appearance: The defogger switch symbol features a front windshield with three upward-waving lines. A semi-circular icon represents the front windshield, while a rectangular icon denotes the rear window. Function: The car defogger switch controls the defogger, which reduces moisture, fog, and frost on the front and rear windshields and exterior rearview mirrors to improve visibility. Notes: The defogger consumes battery power when in use, so always start the car before activating the rear window defogger. The defogger will automatically turn off after 10 to 15 minutes. Once visibility is clear, even if the defogger hasn't automatically shut off, remember to manually turn it off. Avoid prolonged use to prevent damage to the rear windshield.

[ZaneRose]

I've encountered similar issues several times, and there are quite a few reasons why the defroster can't clear the fog. Typically, insufficient cooling from the air conditioning system is the key issue, possibly due to refrigerant leaks preventing the compressor from cooling properly, resulting in poor air dehumidification. If the fan or fan resistor is faulty, the airflow isn't strong enough to disperse the moisture on the windshield. Additionally, a clogged cabin air filter can obstruct airflow, causing fog to accumulate. Moreover, if there's too much dirt or an oily film on the glass, the defroster won't be able to clear it effectively no matter how hard it tries. I remember that long road trip where, due to neglecting AC maintenance for too long, the refrigerant had completely leaked out, leading to dangerously blurred vision while driving. I recommend getting the system and filters checked at a professional shop and developing a habit of regular cleaning to minimize risks.

[DeEllie]

As a driver with 20 years of experience, I've seen many people complain about defogging failures. Most of the time, it's an operational issue. For instance, I sometimes forget to switch to defogging mode—the AC is on, but the airflow isn't directed at the windshield. Or the temperature is set too low, which can cause faster condensation in cold weather. High humidity exacerbates the problem, like on rainy days when the car interior is damp, and weak fan performance can easily lead to failure. Dust accumulation on fan blades or burnt resistors are common issues—I've replaced them twice myself. Maintenance is key; checking the AC filter once a year can prevent most troubles. Remember, preheating the fan for a few minutes before starting helps stabilize the temperature and significantly improves defogging.

[Erik]

I haven't been driving for many years, but it's quite bothersome when the defogger doesn't work properly. The first time I encountered this issue was when I forgot to turn on the air conditioning's defog button, resulting in insufficient airflow. Also, if the air filter is clogged, it can block the airflow, just like that time when there was a lot of dust inside my car, and it improved after cleaning. When humidity is high, fog forms quickly, and the system needs to increase the temperature and fan speed to be effective. If it's a malfunction, it might be due to loose wiring or insufficient cooling, but I'm not very familiar with these technical details. Anyway, it's best to get it checked at a repair shop promptly.

[AaliyahLynn]

I think a malfunctioning defroster is a major safety hazard. I once nearly had an accident on a rainy day due to poor visibility. The reasons include insufficient refrigerant in the air conditioning system leading to high humidity, or a faulty fan circuit preventing airflow. Dirty or oily surfaces on the glass can also block the defrosting effect. I recommend car owners not to delay and immediately check the system to avoid increasing the danger of driving in foggy conditions.