How the Defroster of Your Car Works?

Article by Christian A., on August 22, 2018

When you are driving, you need to have a clear view of the road head. However, there are times when visibility is less than desirable, simply because condensation, frost or ice have built up on the windshield and the rear window. The defroster is especially designed to get rid of these elements to improve the visibility of your windshield and rear window.

Also known as defogger or demister, the defroster helps improve the visibility from the cabin to the outside environment. Condensation on the windshield and rear windows forms because the temperature outside the car is lower than inside the cabin. As the outside temperature gets lower, condensation could turn to frost. To remove the condensation or melt frost, the temperature is raised through the defroster.

Defrosters are generally divided into two types: primary defrosters that are usually installed on windshield defrosters, and secondary defrosters that are found on the rear windows. The activation of the primary and secondary defrosters usually varies on the make, model and year. Nonetheless, the main difference between these types of defrosters is that primary defrosters employ warm air current, while secondary defrosters use electricity to generate heat.

Primary defrosters use the car’s heating, ventilation and air conditioning (HVAC) system to blow dehumidified and warm air on the windshield. When activated, the primary defroster uses the HVAC system to draw in air and flow them through the heater core, thereby warming it. The resulting warm air is directed through the vent on the dashboard to reach the windshield as well as the front windows. Just make sure that the vents are open to allow the warm air to reach the windshield and front windows.

Moreover, a primary defroster removes condensation from the inner surface of the windshield or front windows by passing dehumidified air through the AC system. Dehumidified air can absorb moisture from the windshield and windows, thereby helping get rid of condensation.

A secondary defroster, meanwhile, uses electricity, instead of the HVAC system, to do it job. Installed usually on the rear windows and the mirrors, a secondary defroster makes use of wire grids and resistive heating. When activated, a secondary defroster sends an electrical current to the wire grid, which resistance generates heat. This heat is used to warm up the surface of the rear windows to remove condensation or melt frost. The wire grids of a secondary defroster are usually visible on the rear window as thin horizontal lines running horizontally. On heated mirrors, the wire grids are invisible as they are internally installed.

Nonetheless, you defroster may sometimes malfunction or stop working at all. This could be traced to a number of reasons like:

1. Blown fuse. The fuse connected to the defroster may get blown when a circuit gets overloaded.

2. Clogged vents. Vents direct warm air to the windshield. If they are clogged with dust or debris, they won’t be able to channel the needed warm air.

3. Lack of antifreeze. Your car might not be able to heat properly or enable the defroster to function if the antifreeze levels are too low.

4. Malfunctioning switches. If the switch, button or knobs use to turn on the defroster, then you wouldn’t be able to use this device.

5. Missing terminal edges on the window. When tinted windows have started to crack or their tints are already coming off, the terminal edges could be affected.

6. Disconnected or frayed wires. If the wires linked to the defroster are disconnected or frayed, then the device won't function.

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