How to Clear a Foggy Windshield with the Defroster

You could wipe it away with a paper towel (or, let’s be honest, the sleeve of your shirt), but that poses a couple of problems:

• It comes back almost immediately.
• It leaves unsightly and dangerous smudges across your windshield that obscure your field of vision and cause blinding sun glares.

So what do you do?

Press the defroster…or is it the defogger? Whatever you call it, you push the button with the squiggly lines and wait impatiently…

And voila! By some form of magic, you can see again.

Here’s how it works:

There are two different types of car defoggers.

• Primary defrosters
• Secondary defrosters

Primary Defrosters

Primary defrosters work with your car’s heating, ventilation, and air conditioning (HVAC) system to defog the windshield and front windows by:

• Pulling air from outside of the car into the car’s heater core.
• As air travels through the heater core, it is dehumidified, meaning moisture is removed as the air is heated.
• The now dry, warm air travels through the vents in the dashboard towards the windshield and front windows.
• Warm air wicks moisture from the surface of the windshield as it passes over and removes the condensation that causes a foggy view.

If your car doesn’t have a defrost button, or if it’s broken, fret not!

• Crank up the heat to the highest setting.
• Make sure your HVAC is set to pull fresh air in from outside of the vehicle, otherwise you’ll continue to circulate damp air throughout the car and cause it to stay foggy.
• Blast the air conditioning unit at full speed to keep the warm air moving through your car.
• Crack the windows a little bit to encourage decondensation.

Secondary Defrosters

Secondary defrosters use electric grids across the back windshield or inside the side view mirrors that physically heat the surface of the glass. As the glass heats, the condensation evaporates and clears fog from the surface.