Car Defroster Repair

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Troubleshooting and repairing a rear window defroster is easy, everything you need comes in the Frost Fighter 2700 Master Kit.

Troubleshooting and repairing a car's rear window defroster is a straightforward project that even a neophyte can handle with aplomb. Everything you will need comes in the Frost Fighter 2700 Master Kit. This kit contains all the materials that you will need to repair several auto defroster grids. The kit also come with a test lamp.

This kit has a street value of $70. In cases where the grid is damaged beyond repair, you can replace the entire grid using one of the 2600 Clear View Defroster Kits. More about the 2600 Clear View Defroster Kit a little later in this article. Typically, the 2600 series kits have a street price of approximately $46.

The heater grid

The heater grid consists of a number of thin, horizontal brown lines. Each brown line is a silver ceramic conductor silk screened on the window. The silver ceramic conductors are silk screened on the window and then baked at high temperature to make them more durable. The ends of the silver ceramic conductors are connected together by vertical buss bars. The positive and negative circuit leads are connected to the bus bars by push-on tabs that are bonded to the bus bars. When electric current passes through the grid the individual silver ceramic conductors, they heat to approximately 85°F clearing the window of fog, snow or ice.

Why do defroster grids fail?

A defroster grid fails when the silver ceramic conductors are damaged. The tiniest of breaks in a conductor will interrupt current flow in that defroster grid line. A good indication that the grid lines are broken is when the defroster only partially defrosts the window.

The defroster grid will also fail if the power tabs separate from the vertical bus bars. The tabs may also be knocked loose accidentally. The Frost Fighter 2700 Master Kit contains everything that you need to replace the tabs and the connectors associated with them.

Age can cause some of the older grids to lose their conductivity. The only solution for this is to replace the entire defroster grid. The 2600 Clear View Defroster Kit contains everything that you need to replace the grid.

Window tint is another cause of defroster grid failure. Window tint does not become a problem until the film is removed. The tint film often binds tightly to the silver ceramic conductors, pulling them from the window when the film is removed. If the defroster stops working right after the tint film was installed, suspect that the installer accidentally cut one or more of the lines.

Troubleshooting: Checking the fuse, switch, timer and relay

The defroster circuit is a high amperage circuit and is fused for protection. To save time always check to see if there is power present on the main bus bar tabs before looking for breaks in the grid. Most rear window defroster switches have a built in light that comes on when you turn the defroster on. If the light comes on you know that the circuit fuse is good. If the light does not come on check the fuse. If the light is on, check for voltage at the bus bar power tabs. If there is no voltage present on the tabs, the defroster switch, timer, or relay is bad. Locate these components using your car's service manual and check them with a test light, such as the one that comes with the Master Kit, or with a digital multimeter. These components can fail, but the problem usually lies with a blown fuse or the defroster grid itself.

Checking the grid conductors

Each of the silver ceramic conductors are in effect linear resistors. Place both of the test light probes at the end of one of the grid lines on a bus bar. Slowly slide one of the test probes toward the other bus bar. If the grid line is intact the light will slowly grow brighter until it reaches maximum brilliance when the probe is resting on the second bus bar. If there is a sudden change in brightness, that grid line is faulty.

How to repair a damaged grid.

The master repair kit comes with detailed instruction on how to use the various epoxies and conductive paints to repair the grid.


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Posted on Feb 25, 2011
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