Cars are full of weird, quirky mysteries. There are small panels on the bumper, hairs on tires, and shark fins on the roof. Another detail many drivers have probably noticed without giving much thought to is the set of thin brown or orange lines running across some rear windows. Here’s what those lines actually do, why they sometimes stop working, and what can damage them.
What Are the Lines on a Rear Window and How Do They Work?
Those lines are part of the rear defroster. When it’s turned on, electricity runs through them, warming the glass enough to clear fog, frost, and light ice. Some vehicles also turn on heated side mirrors with the same button.
Ford Motor Company advises using the system while the vehicle is running. “Make sure the engine is on before operating the heated rear windows,” according to Ford.
The front windshield usually clears differently. Warm air from the car’s heating and ventilation system blows onto the glass, so most windshields don’t need the same visible lines.
Heated windshields do exist. AGC Automotive makes versions with very fine wires built into the laminated glass. Some heated windshield designs can target areas such as where the wipers sit.
Why Rear Window Defroster Lines Can Stop Working
The thin lines can get damaged, especially when something scratches the inside of the rear glass. A break in one line may leave a strip of fog or frost behind while the rest of the window clears. Sharp tools, rough cleaning, and removing decals can all cause damage.
A broken line doesn’t always mean the entire rear window has failed. If none of the lines heat up, the problem may be elsewhere in the defroster system rather than with the lines themselves.
The inside of a heated rear window needs a little extra care when it’s cleaned.
“Do not use harsh chemicals, razor blades or other sharp objects to clean or remove decals from the inside of the heated rear window as this could damage the heated rear window gridlines not covered by the vehicle warranty,” according to Ford.
Subaru also warns against using sharp tools or abrasive cleaners on the inside of the rear window. Drivers should also avoid scraping the glass when removing decals because that can damage the lines.
Are All Lines on the Rear Window Part of the Defroster?
Not every line on a rear window necessarily produces heat. Some vehicles also have radio antennas built into the glass.
General Motors service information for certain vehicles states that some upper lines can serve as an AM/FM antenna rather than as part of the defroster. The owner’s manual can show what the lines do on a specific vehicle.
Most of the horizontal lines covering the main part of a rear window, however, belong to the defroster and warm the glass when the system is turned on.
Sources
- Ford Motor Company, “Switching the Heated Rear Window On and Off”.
- Subaru, “Owner’s Manual”
- Subaru, “BRZ quick guide”
- General Motors, “Rear Window Defogger Description and Operation”
- AGC Automotive, “Heated Wire Windshield”
- General Motors, “Service Bulletin”
The post Those Lines on Your Car’s Rear Window Aren’t Just for Decoration — Here’s What They Do appeared first on Family Handyman.
Article source here: Those Lines on Your Car’s Rear Window Aren’t Just for Decoration — Here’s What They Do
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