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

P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...


Related questions

Q: Fan wont blow out top vents for defrost.

Hi there. Check the blend doors to the vents and see if they move when the switch is turned. If they do not move, then check for a vacuum hose to the blend door actuator. If there is no vacuum...

Q: My air conditioner blows warm when idle, looses coolant and starts to overheat.

Hi! I have a couple of thoughts that may help you sort out the issues with your Explorer. There may be separate root causes of the issues with the air conditioning system and the cooling system. The first thing...

Q: How Does a Car's Rear Defroster Work?

Most vehicles have an electrical grid on the rear window that will warm the glass to clear fogging or frost. The rear defroster grid is applied to the inside of the glass by the manufacturer and actually conducts electrical current...