There is no need to enumerate situations in which the “blindness” of the rear window turns into trouble. The reasons for the cessation of heating are as diverse as any other incidents in electrical engineering. Recall the most common trouble - damage to conductive threads. Often (almost always!) The owner of the car is to blame for this, more often - his wife, accustomed to putting purchases under the rear window. Often the threads are damaged by careless washing or cleaning the glass from the inside. The threads are tender - a single scratch may be enough for failure. When there are several of them, you will understand that it is time to repair them. Do not change the glass!
There is a cheaper solution: buy a composition for repairing a heater (price from 60 to 170 rubles). Now the most interesting thing is to find the damaged places of the heating threads. The fact is that defects are not always visible to the naked eye. But this is not required if you have a vertebral probe - the first assistant to an electrician. Turning on the heating of the glass, we fix the clamp of our appliance on the car body (“weight”), and carefully move the probe along the failed thread (see. Fig.). At the point of the cliff, the probe’s glow changes from red to green as it moves from plus to minus. In the opposite direction - from green to red. But if the thread is intact, then the picture is different - the color gradually changes from one to another. Gap found. It remains to restore the conductivity. The repair kit has a brush and a special template that helps to very carefully apply the repair composition to the right place. It dries in 20-30 minutes - after which the heater is ready for use.
Conveniently? But there were times when there was nowhere to buy conductive glue. Everyone survived to the best of their imagination. My colleague began the experiments by mixing varnish with aluminum powder, and quickly realized that science was not deceiving. The "conductivity" of this composition at a voltage of 12 V … none. The experiments ended in complete success when the “powder” of natural, 583nd test, gold came into play! This material was conducting current. But the family council decided that buying a new glass would be cheaper and more reliable. People did not do more pragmatic experiments - when breaking the threads, they simply changed the glass.