Why your car defroster or defogger is not working?
A faulty defroster or defogger may not seem like an urgent issue until you’re stuck in a freezing car with zero visibility. This component is not simply a luxury but a necessity, so you can see the road. In this guide, we tackle the top reasons your car defroster or defogger fails to perform.
How do defrosters and defoggers work?
Most people use the terms “defogger” and “defroster” interchangeably. For this blog post, we’ll use “defroster” for clarity.
However, defrosting and defogging are two separate processes that help clear fog, frost, and condensation from your front and rear windshields. Although they serve a similar purpose—maintaining visibility in your vehicle—they work differently.
Defrosting is the process of warming the windshield and rear window to remove exterior ice and frost buildup.
Defogging clears interior humidity from the cabin to reduce fog that forms inside your car.
Although you need both to see clearly, how your car clears the windshield and the rear window differs.
Clearing the Windshield
Your car’s HVAC system both dehumidifies the air in the cabin and warms the front windshield to remove frost. To defrost, the HVAC system directs warm, dry air toward the windshield using dashboard vents and pulls heat from the car’s engine coolant to evaporate fog and melt ice or frost. This process also dehumidifies the air to remove fog.
Clearing the Rear Window
The rear windshield uses thin heating elements applied to the window to generate warmth and eliminate frost. Fog removal is carried out inside by the HVAC system, since fog forms inside the cabin.
Why don’t cars have just one system?
Airflow can become obstructed in some enclosed spaces like the back of the vehicle, which is why the rear window uses electrical elements rather than the HVAC system. The glass is also a different kind from the “safety glass” that the windshield is made of.
You can find some vehicles with the heating elements applied to the windshield, though. When you test drive these, ensure your visibility is unimpaired.
Why is your front defroster or defogger not working?
Different causes can result in a malfunction in your front defroster or defogger. We’ll cover some of those here.
Heating system problems
If you’re experiencing problems with your defroster and generating heat within the cabin, the issue likely lies with your car’s heating system.
Your car’s defroster relies on your vehicle’s HVAC system, which uses coolant to generate warm air. If your coolant level is too low, the defroster will not have enough warm air to clear condensation and frost. Having your coolant level assessed can often resolve this issue.
A faulty thermostat, malfunctioning heater core, blower motor failure, or mode door actuator issue will render your car’s heating system and your defroster or defogger ineffective. These problems should be handled by a trained automotive technician.
Clogged vents
Your car’s defrosting vents, which are directly aimed toward your window, require proper airflow to the windshield. Clogged or blocked air vents will prevent the functionality of your defroster.
Wrong setting
If your defroster takes too long to clear the windshield, check that your defroster is set to a fresh air intake mode for faster results, because recirculation mode will only keep the humid air inside the cabin and increase fogging.
Buildup on wipers
Sometimes, a strong build up of grime, salt from trucks you’ve driven behind, and other dirt can hinder your wiper blades in clearing your windshield or rear window.
Thankfully, this is an easy and inexpensive fix. Upgrading to winter wiper blades and using a windshield washer fluid designed for winter can help maintain the functionality of your wiper blades and help the defroster or defogger work effectively. An AUTOPRO technician can take care of these tasks for you.
Why is your rear defroster not working?
The back defroster relies on several electrical components to clear snow and frost, any of which could malfunction.
Electrical system issues
A surge or short circuit can also cause the fuse to fail. If you feel comfortable doing so, you can check your car’s fuse box and replace any blown fuses to restore function in the defogging circuit.
Other issues are best examined by an automotive technician.
Any scratched or broken gridline in the wiring will not effectively conduct electricity. This could lead to uneven or incomplete defogging of the rear window.
Similarly, the relay in your vehicle’s electrical system will control the power distribution to the defroster. If the relay fails, the rear defroster will not receive power.
The small terminals the rear defroster uses to connect to your vehicle are at the sides of the rear window. Loose or corroded connections can also lead to problems.
Ultimately, if any wires are damaged or disconnected, electricity may not reach the defroster. Inspecting and repairing the wiring related to relay, fuse, and grid lines will determine if your electrical defroster’s system has been compromised.
Other possible issues
If the rear defroster is not working, it could be due to a dirty windshield rather than an electrical issue. Giving your windshield a good clean can clear this problem up right away. Similarly, excess grime or dirt may reduce the effectiveness of the rear defroster.
Aftermarket tinting can also damage the gridlines and interfere with conductivity. If you believe this to be the case, speak with an automotive technician to determine if a repair is possible.
If you feel at all unsure about why your defroster or defogger isn’t working, visit your local NAPA AUTOPRO service centre for an assessment. Our automotive experts will be more than happy to help.