A functioning defrosting system is key to getting around on a frozen morning. Some of the issues that require defroster repair are more in depth than the scope of this article and may require the assistance of a seasoned mechanic, but there are a few common defroster problems that can be easily diagnosed and repaired at home.
Signs of Failure
When you’re warming up your car on a cold morning, you may notice that while most of the glass is defrosting, there are some sections that remain icy. Or perhaps the defroster’s been on for a while and nothing is happening at all. These are both signs of defroster failure, which could be caused by natural wear or something you did. Be mindful that you should never scrape the defroster grid and that cargo can accidentally bump into it, causing scratches or breaks in this fragile electrical system.
When you’re figuring out what’s going on with your defroster, checking for a burnt fuse is a good place to start. However, if the entire defroster isn’t working, it could point to a more complicated problem.
Before consulting a mechanic, do a visual inspection to rule out a common source of defroster trouble: broken tabs. The defroster grid is a series of parallel wires that run from one side of the rear windshield to the other. Power is brought indirectly from the battery to a metal tab on one side of the windshield while a tab on the other side of the glass connected to ground. If one or both of these tabs is disconnected, the circuit will be incomplete and there will be no heat.
Tabs can be easily reattached using tab adhesive, a specific type of glue that contains conductive properties to carry a current. Before application, clean the area with alcohol — again, careful not to scratch the grid — and if necessary, remove stubborn residue with sandpaper. The key to repair is getting solid contact between glass and tab, and even a little residue will derail a proper fix.
Most kits require you to mix the adhesive before application, so follow the instructions on the package. Next, using a toothpick or the provided tool, spread the mixed adhesive onto the glass and the back of the tab. Attach the tab to the glass and hold for a minute or so. The adhesive will only cure well in warmer temperatures, so you might want to use a hairdryer on it for a few minutes if you’re working in a cold environment.
Off the Grid
Disruptions in the defroster grid might also be caused by scratches that are too small to see, so you’ll need a test light for diagnosis. With the vehicle and defroster on, clamp the light onto a solid metal ground point and test each line of the grid separately. You’ll be able to find the inoperative lines where your test light doesn’t illuminate.
Once you’ve identified the problem lines, move the light down the wire an inch at a time to find the exact point of breakage. Clean the area well, and ready your defroster repair kit. Kits usually consist of conductive paint and a masking template to reduce the risk of over-application. Place the template over the damaged section of grid, and brush on two coats of paint. Let the paint dry, and you can usually use your defroster within an hour. It’s an easy DIY fix that’s certainly cheaper than window replacement.
Check out all the electrical system products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on defroster repair, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photo courtesy of Blair Lampe
Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.