Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. How Does a Defroster Work?

How Does a Defroster Work?

defroster

We’ve all been there. You slide behind the wheel, crank the engine and then stop. You realize that you really can’t go anywhere because your windshield is fogged up. Thankfully, you can just turn on the defroster and let your car do the work of clearing away that unwanted moisture for you.

How a defroster works

Your car’s defroster is tied into the air conditioning system. While that means it can get 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 furnace was removing too much moisture from the air, you’re already familiar with what’s going on here.

Your air conditioner (whether it’s set to cold or hot) condenses the moisture out of the air into water. This condensation is vented through a drain hose that runs from behind your glove box out the bottom of the car. The system then pumps dry air into the car. When you turn on the defroster, it pumps dry air up toward the windshield. This helps to evaporate the moisture.

The right temperature

Sometimes, different temperatures are needed. For example, you may notice that cold air works better during the summer and warm air works better during the winter. This is simply due to the outside ambient temperature. Your defroster (in addition to drying the humidity from the air) is also equalizing the temperature of the glass and the interior air to some extent.

Unfortunately, this also means that if your air conditioner isn’t working properly, your front defroster won’t work right either. It may either only slightly clear the moisture from the glass, or it may not work very well at all. Generally, this is caused by low refrigerant levels in the air conditioner.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
Veteran and Military Driver Laws and Benefits in New Mexico
The state of New Mexico offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch...

Related questions

Q: How Does the Front Defroster Work in a Car?

Selecting the front defroster mode directs warm air up through the ducts at the base of the windshield in order to clear moisture in warm weather or frost in colder temperatures. In cold weather, the defroster becomes more effective after...

Q: Need to know the A/C relay location on a 1982 European Mercedes-Benz 280sl.

The relay is on the driver side right next to the brake booster and master cylinder. It looks like a large black block by the fender. For the compressor to not have power to it, check the low pressure switch...

Q: Defrost button wont come on. Control power button doesnt work.

It seems like the defrost of the vehicle has an issue. There are several possibilities that could cause this. The control unit for the climate control system could be malfunctioning. The fuse for the rear defrost could be blown due...