In frosty weather, if the glass of your car is fogged up or covered with a layer of frost, turn on rear window defogger: this will improve visibility and provide safety on the road. After turning on the heater should light up the corresponding indicator located on the dashboard of the car. A few minutes after turning on the heating system view on the rear window: it should be cleaner and more transparent, and the snow on the outside of the machine will begin to melt. Put your hand on the glass. If heating works correctly, you should feel the warmth.
If the indicator work heating shows that the work began, but the glass is still covered with perspiration, check if the fuse for the heated rear window. Turn it off if necessary.
If the glass is not frozen, and on the surface of the car there is no snow, use the following methods to check the rear window defogger. Sit in the back seat and forcefully exhale with your mouth on the glass. It should fog up, and immediately begin to clean, warm lines of heating.
Standing outside the vehicle, on the rear glass pour a little water. Properly working heater will not allow water to freeze on the glass even in the dead of winter. If the failure happened only some threads of the heated glass is heated unevenly, with water is easy to calculate exactly what the band need replacement. Pour the glass of water and see what areas of the glass it froze. If you don't have water, try to jot down on the glass a little bit of snow.
Fans to rummage in the car and check the operation of all contacts can try the following method of test. Turn the rear window defogger. If the indicator shows its working, the relay properly, disconnect the contacts of the heater on one side of the glass and connect them together through a "probe." If the heater is working properly, current will freely pass via the threads of the heater, causing the probe will light up. If the probe becomes brighter, faulty filament heater or oxidized contacts.