How do heated windows operate?
Heated windows are made of glass with a conductive resistance panel that is either installed on the surface, or molded integrally into the glass. They offer the ability to defrost, or or de-ice a frozen or foggy window or windshield.
The heater for the windshield is usually for the top of the windshield, or for the bottom edge, in order to keep the wipers from freezing. The heating element is activated or controlled by a switch that turns the circuit on, and a computer or timing circuit that controls the length of time that the heater operates.
The rear window typically uses a heating grid technology to defrost or de-ice the window, and is readily noticed by the lines across the length of the glass. This is similar to the technology used for heater sideview mirrors.
The proper operation, or clearing effect provided, depends on the integrity of the conductive element. On late model cars, attention should be paid when cleaning the window as the conductive strip can be damaged, causing part of the heater element to fail; you can feel the conductive strips when cleaning the glass. It is best to clean side to side and avoid up and down movement over the element strips, which can lead to damage.
Heater element damage is easy to notice when turning on the rear defroster heater because you will see some sections of the window clear, and others that do not. The areas that don’t clear are the spots where damage has occurred.
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