Why Your Car Won’t Defrost Windows


It can be a small aggravation but having a car that won’t defrost is not something you need to deal with on a cold morning getting ready to go to work. The problem could be something minor or it could be a major issue. 

The basic problem of why car won’t defrost is that the heater isn’t working. However, there could be an array of issues within that category from buttons not properly pressed, blown fuse, or a bad speed controller. 

Read below to see if one of these nine problems can address your defrost issue. 

Defrosting Your Car

The first thing to understand is how frost accumulates on your car. This can happen any time of year but frequently occurs when it’s cooler weather. It happens when the water vapor freezes on the windows and that typically happens overnight. 

Defrosting occurs when the inside of the car becomes warmer than the outside. Warm cabin air can also cause it to be foggy on the inside of the windows, which also requires the defroster to be used a different way. 

Warm air defrost icy windows but you will need cooler air will get rid of the fog. Cooler air on the windows lowers the glass temperature and creates a balance between the warmth inside the car and the glass. That ends the fog.

9 Things to Check When Defrost Doesn’t Work

Several things can contribute to an improperly-working defroster. The first items are super easy to figure out and can get you on your way quickly. Most of these problems can be fixed on your own and cost nothing to little to repair.

Check Buttons and Knobs

The most common problem is that a button or knob was turned during the day that needs to be turned back to properly defrost the windows. This especially happens in areas where temperatures vary throughout the morning, day and night. 

Checking the buttons and knobs to make sure they are on the correct selection will save you some aggravation on a cold day.

Buttons and knobs can also get stuck sometimes. Cars get dirty and dirt and grime in crevices can create the situation. Keep pressing and turning until the button or knob turns easily to the correct position. 

You will need to clean the areas around the buttons and knobs to keep them from sticking. You can do this using rubbing alcohol and a cotton squab.

Fuses Need Replacing

Another common problem relating to a defroster is a blown fuse. You can check this by using a voltmeter to test fuses and then replacing the malfunctioning one. 

This is something most people can do themselves using the fuse diagram in the owner’s manual identifying the fuse for the defroster. 

Most of the fuse boxes are located under the steering console. They come numbered and the number will correspond with the diagram in the owner’s manual.

Related About Fuses: Why Won’t My Windshield Washer Fluid Come Out?

Check Your Window

There are several types of issues that could be happening with your window when the defrost isn’t working. A common issue could be missing the terminal edges on the heat grid installed in the window. 

Another issue is the window tint. A cracked tint or one that is peeling off can cause problems with the terminal edges and that will affect the defroster.

You should also check for cracks and stars in the window as that can also disrupt terminal edges and how the defroster works.

Something else to look at when you examine the window is a damaged grid. This would cause a defroster to fail. A mechanic will likely need to help you with this but some handy people can fix this on their own.

Check the Battery

Battery issues can be attributed to many car problems including a non-functioning defroster. It could be the battery if other functions, like lights and the radio, aren’t working. You can try jumping off the battery to see if that gets your defroster and other things working.

A jump start is just a temporary fix. You may need to replace the battery if it’s old or if the problem keeps happening. Some retail auto stores will check a battery for you to see how much life is left.

Read: How Long Can a Car Battery Sit Unused?

Check the Vents

Another common issue could be a vent clog. The vent beneath the window is where the warm air comes from and blows onto the window. Moving the vent around, opening and closing it, can unclog it. You may want to dust or vacuum it to permanently solve the problem. 

Look for Frayed Wires

It’s possible for wires connected to the glass may be loose, disconnected, or frayed. A temporary fix is to use electrical tape to keep them from fraying worse but you will need to replace them soon. 

Wiring can be tricky to fix because improperly fixing it can cause a fire. Be sure to check for instructions before you tamper with wires as a quick fix to your defroster problem.

Find the Harness Connector

The harness connector can become loose and may need to be secured. This is usually found on the back of the driver’s seat. 

Examine Your Electrical

Buildup and dirt can accumulate on electrical wiring and connections. Check the connections to see if this has happened. You can clean terminals with rubbing alcohol a rag or cotton swabs and then try to run your defroster. 


Serious Problems

Beyond these simple issues, you could have a serious problem affecting your defroster including a bad blower speed controller or a blown defrost motor. Either or both will need to be replaced if these are the problems. 

How to Defrost My Windows Quicker?

Most people turn on their heat and defrost onto high and use their recycle button to quickly thaw their windows. That will create fog on the inside of the window, which will need to be corrected. 

Some suggest you can turn on the defrost without heat and open the windows to get rid of the fog quickly. However, that can be uncomfortable if you are waiting in the cold.

Defrosting quickly can happen more comfortably by using the defrost button while avoiding the recirculate button to bring in dry air and pushing out humid air. 


One interesting tip from mechanics to prevent defrost problems is to keep your windows clean. Believe it or not, but clean windows fog and frost less often than dirty ones. The type of wipers you use can also help keep your windows from frosting over.

Certain brands may cost more but the chemicals they use on the wipers will go a long way to keeping moisture off your glass.

You can try to resolve the defrost problem by checking out these common problems. A mechanic should look at your vehicle should these fixes not remedy the problem as it could mean a more serious issue like a blown defrost motor. 

Even a blown defrost motor doesn’t cost that much to fix. The parts cost between $15 to $30 and the labor will cost between $30 and $50.

It’s always best to allow enough time for your car to defrost and warm up before you drive it. That will make for a more comfortable ride for you and is better for your car. 

Leave a Comment