How does a defroster work?

We've all been there. You get behind the wheel, start the engine and then stop. You realize you can't really go anywhere because your windshield is fogged up. Luckily, you can simply turn on the defroster and let your car do all the work of removing that unwanted moisture for you.

How a defroster works

Your vehicle's defroster is connected to the air conditioning system. While this means it can be quite warm and very cold, it also means something else. If you've ever had to use a humidifier in your home during the winter because your stove was removing too much moisture from the air, you'll already know what's going on here.

Your air conditioner (whether set to cold or hot) condenses moisture from the air into water. This condensate is removed through a drain hose that runs from behind the glove box in the bottom of the car. The system then blows dry air into the vehicle. When you turn on the defroster, it blows dry air to the windshield. This promotes the evaporation of moisture.

Correct temperature

Sometimes different temperatures are needed. For example, you may notice that cold air works better in summer and warm air works better in winter. It's just because of the outside ambient temperature. Your defroster (in addition to drying the moisture out of the air) also equalizes the glass and cabin air temperatures to some extent.

Unfortunately, this also means that if your air conditioner isn't working properly, your front heater won't work properly either. It can either only slightly clean the glass of moisture, or it may not work very well at all. This is usually caused by low refrigerant levels in the air conditioner.