Finding a Cheap Fix for a Broken Defroster

Frozen foggy windshield
Rolfo / Moment Open / Getty 

There are two kinds of car defrosters, so the answer to your question depends on which one you’re talking about. One of them uses air from the car’s HVAC system to melt ice and to clear foggy windows, and the other uses a grid of hot wires. There are potentially cheap fixes for both types of broken defrosters, but it really depends on exactly how it's broken in the first place.

Just to be safe, we’ll look at both kinds of broken car window defrosters and try to cover all the bases.

Front Windshield Defroster Fixes

When you turn on your front windshield “defroster,” all you’re really doing is switching the HVAC blend door to direct air out of the dash vents. If this defroster stops working, then it’s either a faulty switch or blend door (if air comes out of the other vents), or a bad blower motor. The cost and complexity of those repairs depend on the vehicle, since some heater switches, blower motors, and blend doors are easy to get at, and others require you to remove the whole dash assembly.

Keep in mind that if your heat isn’t working, that doesn’t necessarily mean that your front defroster is also busted. Although blowing cold air from your A/C on your windshield isn’t going to melt any ice, it does effectively lower the relative humidity inside your car, which will do a fine job of defogging your windows on a cold, rainy day.

Rear Window Defroster Fixes

Unlike front windshield defrosters, rear window defrosters are actually dedicated devices that can (and do) break. They are relatively simple wire grids that receive power from the car’s electrical system when you flip the defroster switch. When electricity flows through the grid, the wires heat up, which causes ice to melt and condensation or fog to dissipate.

The most common cause of a rear defroster failure is a break in continuity or a short in the defroster grid. The easiest way to check for this is to use a voltmeter or a test light to look for power and ground and to use an ohmmeter to check for continuity along each line of the grid. Another common point of failure, in hatchbacks, station wagons, and some SUVs, is the actual spade contacts where the power and ground are hooked up. Of course, it’s always possible for a switch to go bad as well.

When a rear window defroster goes bad, the repair is typically either expensive or time-consuming. Cheap repair kits can sometimes take care of continuity breaks, and aftermarket replacement grids are also available, but it is sometimes necessary to replace the back glass altogether.

See more about: troubleshooting and fixing a rear defroster

Car Defroster Alternatives

In the case of front windshield defrosters, both heat and air conditioning can do the job of defogging your windows, so the best alternative is to just try the one that’s actually working—if either one is. Air conditioning gets the job done since the process of cooling air via and a/c unit pulls moisture out of it, but hot air is capable of holding more water than cold air, cranking up the heat will also heat up the glass of your windshield and prevent the moist air in your car from condensing there. Of course, you’ll want to keep your recirculation off if you’re using this method.

Electric car heaters can also do the trick, regardless of which type of windshield defroster you’re trying to replace. Although you’re unlikely to find a 12v or battery-operated heater that’s capable of replicating the heat output of your car’s heater core, some of these units are pretty good at defrosting and defogging windows.

If nothing else works, you can also check into 12v car defrosters.