You may be surprised by the topic of today’s article, because it’s summer and the weather is replete with sunny, hot days. But this function is relevant at any time of the year. Let's talk about heated rear window. For those who think this is completely unnecessary in the summer, you probably don't get around by car much during the rainy season.
But here’s the problem, Mr. Murphy comes into play with his notorious “laws of meanness.” It’s raining outside, and the heated glass has stopped working, and the humidity in the cabin is increasing and visibility is decreasing. The car's rear window heating is urgently required to be repaired. The reasons for such an unexpected trouble can be a variety of actions, from the lack of professionalism of the tinting studio service workers to the pranks of children in the passenger seat.
Rear window defroster: how does it work?
Heated rear car windows do an excellent job of eliminating fogging and do not dry out the air in the cabin. Regarding thawing glass in winter, the advantages are obvious. The car glass evenly gets rid of icing by the time it needs to be pulled out. The air from the heater has just begun to warm up, and the rear window is already clean, dry and transparent.
Rear window defroster: what is it and what is it for?
The most effective fighter against fogging of car windows is heating. How does the heated rear window work? The windshield is heated by directed warm air flows. The rear window is heated using small heating elements powered by electrical energy. Metal tracks with high resistance in the form of multiple thin ribbons are attached to the glass itself from the inside (from the interior). When electrical energy passes through them, heat is generated. As a result, the glass heats up and the water evaporates. After a few minutes the glass becomes transparent again.
In order to successfully diagnose malfunctions and repair the heated rear window of a car as professionally as possible, it is necessary to study the electrical diagram for connecting the heating elements and understand its working principle.
The image shows a typical diagram of connecting heating to a car's electrical wiring. Let's figure out together how it works. Power comes from the “+” terminal of the battery, passes through the ignition switch, fuses and is supplied to the heater controller and the power contact of the relay. The battery terminal with the “-” sign is connected to the car body, as is one of the terminals of the heating device.
When the heater is turned on, the voltage goes to the winding of the relay, which is triggered, the power contacts are closed and the relay terminals 30 and 87 are interconnected. The current goes to the heater, flowing through parallel-connected threads, and then through the car body again goes to the minus of the battery.
What kind of malfunctions can there be?
Basically, car owners do not bother with what and how this rear window heating device is used until it fogs up or becomes covered with an ice crust. Here, with the usual movement, the button to turn on the heating power is pressed, five minutes, ten, fifteen pass, but there is no result: the glass has not become any more transparent, or the view has appeared only in some part. Here, no measuring instruments are needed to understand that the rear window heater of the car requires repair.
Please note that the heater turns on only when the ignition key is turned to the “ON” position. In other cars, the heater turns on only when the engine is running. This is done in order to avoid premature battery discharge. Depending on the car model, the rear window heater can consume from 10 A to 25 A of electric current. To give you an idea, two car headlights consume 10 A.
Rear window defroster does not turn on
If the light on the heating button does not light up when it is active, the button itself is most likely faulty or the fuse has blown. If the light is on, but the filaments do not heat up, then the reason lies either in the relay or in the connectors connecting the device to the on-board electrical wiring. If this case occurs, then using the vehicle documentation you should determine the location where these parts are located and replace the non-working element. It is not always possible to quickly find the location of the relay, but there is one way to check its functionality indirectly. We'll talk about this a little later.
The rear window is slowly fogging up
Sometimes it happens that after the heater is brought into a state of activity, the glass begins to fog up, but very slowly. If the weather is frosty outside, then the reason may lie in insufficient contact of one of the connectors of the electrical circuit. As a result, contact resistance increases, less current flows, power decreases, and the filaments heat up more slowly.
To check this malfunction, you need to take a multimeter and measure the voltage at the heater and battery input terminals. The difference in results should not exceed one volt.
Horizontal streaks of fog remain on the rear window
And, perhaps, the most common malfunction of the rear window heating system of a car is the breakage of the threads attached to the glass itself. This malfunction is visible to the naked eye, since at the location of the faulty element the glass is either fogged up or not thawed (depending on the time of year).
Paths carrying current are easily destroyed even with minor mechanical impact. Therefore, you cannot clean the glass with a scraper, only with a soft cloth. Also, if you sometimes transport long or large cargo, they should not rest against the rear window.
Diagnostics and repair
Identifying a damaged heater filament is not difficult, as you already understand. Therefore, before you repair the heated rear window, you need to count all the threads from top to bottom and remember which ones are faulty. So, with a visual inspection, it will be easier to find the right thread. But sometimes the gaps are simply microscopic. A voltmeter or multimeter will help here. To quickly find the problematic thread, you need to study the rear window defroster device.
Ways to find a problematic thread
If visual signs of a break are not observed, for example, if a break occurs at the terminals, then you can resort to the good old folk methods. The remarkable thing is that every motorist, with the slightest effort and expense, is able to find the place where the heater filaments break.
Visual diagnostics. If the rear window is foggy, turn on the defroster. At the point where the threads break, it begins to sweat almost immediately, when the rest of the damaged element does not warm up.
Using a voltmeter is the first method. Turn on the ignition and then the heated rear window. Place one probe of the device on the ground of the car, wrap the second one in foil and move it to the center of the heating filament. The voltage should be no more than 5 V. Where it drops to zero or jumps to twelve, there is a break.
Using a voltmeter is the second method. Place one probe on the positive terminal of the heating element, and move the second along the thread from the side of the negative terminal. In a place where the voltage drops to zero, repair of the heated rear window is required.
Using an ohmmeter. It is better to take an analog device with an arrow. Turn it into kilo mode. Place the probes on the opposite terminals of the system. Soak cotton wool in distilled water and slowly move it along the thread. In the place where the instrument needle twitches, there is a break.
That's it, the diagnostics are done. Now, inspired by your successes, you can take on repairing the heated rear window yourself.
We carry out repairs
There are many options for repairing a rear window defroster. The same can be said about the materials used and the techniques used. In any case, you are free to choose the method of carrying out repair work. There is only one thing to remember: in any case, the connecting points of the heating system must always be cleaned and degreased if soldering is required.
1. How to repair the heated rear window using a repair kit? Many car rear window defroster repair kits have similar features. With their help, you can restore up to ten centimeters of a heating filament that is damaged. The repair kit includes: templates with threads and a cylinder with thermally active polymer resin.
Determine the location of the thread break and turn off the heating device. Remove the protective film from the template and attach the thread to the broken area. Using a brush, apply the polymer material to the area to be repaired. When dry, repeat several more times. Remove the stencil from the glass and do not turn on the heating for 24 hours.
2. How to repair a rear window defroster using conductive paste? It is applied to the places where the threads break. At the same time, grab the torn ends on both sides, 2 cm on each side. The paste should dry for a day. You can use a hair dryer and speed up the drying process.
3. Restoring rear window heating tracks using traditional methods. In principle, they themselves do not differ from each other, only there is a difference in the materials used.
Paint and shavings. The shavings are extracted using a file and a copper-brass block. It is better to take paint to match the color of the heating threads. Mix the ingredients in a 1:1 ratio until it forms a soft dough. Make a stencil from tape or tape. Turn on the heat and apply the mixture using a stencil. You will hear about the presence of contact at the repair site by a characteristic light hissing sound. All is ready. You can go straight away and not wait a day.
Glue and shavings. Here, instead of paint, BF-2 glue is used, as an option.
Soldering the break point. Here you need to use zinc chloride. Solder should be taken with a low tin content, such as POS-18, POSS-4-6. If a long section of the heating filament is damaged, you can use a silver or copper wire.
Now you should have enough options on how to restore your car's rear window defroster yourself. As you already understand, this will not cause much difficulty, and you don’t need to spend a lot on materials.
Today, all cars are equipped with a heated rear window system. Thanks to its correct operation, it will be easier for the driver to perform maneuvers, since he will know what the situation is behind the car. What malfunctions can occur during operation and how to repair the heated rear window yourself? Find answers to these and other questions below.
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Description of the rear window defroster
So, what is the device for heating the windshield or rear window and what is the purpose of this system? The device is used to defrost ice at sub-zero temperatures, as well as remove fog in the car in wet and dry weather. Special threads are applied to the rear window to remove any remaining ice while the car is warming up in winter. By the way, a heater is considered one of the most effective ways to combat fogging.
A certain number of special conductive filaments on a special film are installed on the rear window. This film is fixed with glue, and the threads themselves operate on electricity. Electricity passes through the threads, allowing it to release heat and, accordingly, heat the glass itself.
Working principle and functions
The principle of operation of a car window heater is that the driver presses a button located in the vehicle interior and further heats the glass. The power to the system itself comes from the positive terminal of the car battery - the voltage in this case is supplied through the safety elements and the ignition switch. Ultimately, the energy is supplied to the device controller, as well as the relay contact. The negative contact of the system is connected to the ground of the vehicle, that is, its body.
When the system is turned on, voltage is supplied to the relay coil. When this element is triggered, the contacts close, and two terminals are simultaneously connected, which are marked on the diagram with numbers 30 and 87. Then the energy is transferred to the heating system and supplied to the threads, which are fixed on the heated glass with glue. Next, the current flows again through the grounding of the machine and goes to the negative output of the video - Sergey Kotov).
Possible malfunctions and their symptoms
As practice shows, often if the heating system does not work, car owners find out about it as a result of fogging or the appearance of plaque. A person turns on the heating, but either there will be no result at all, or the surface will warm up, but minimally and unevenly. The power supply circuit of the system may be different - in some cars it is activated without turning on the ignition, in others the key must be turned in the lock.
Before checking and repairing the system, we recommend that you familiarize yourself with the list of faults:
- The device does not activate. As a rule, there is an indicator on the activation button - if the light does not light up when it is turned on, then the problem must be looked for either in the button itself or in the safety device. If the indicator is on, but the device does not function, you can also check the relay.
- If the CO works, but the glass itself warms up too slowly, which is especially important during frosty periods, then perhaps the reason should be sought in the connectors. If the contact is poor, then its resistance may be higher, and the voltage value will correspondingly become lower. As practice shows, often the cause of a malfunction lies in poor contact of the CO with the vehicle’s on-board network, so the contacts should also be checked.
- Another problem is that after CO activation, horizontal marks remain on the surface of the car glass after some time. In this case, the reason appears to be damage to the threads in certain places. A malfunction of this kind can be determined without testers - just by eye. It should be borne in mind that threads can be destroyed even with minor impacts; quite often this happens as a result of using a scraper for rubbing.
Photo gallery “Damaged sections of CO tracks”
Diagnostics and repair
Now let’s learn more about how to diagnose and restore the damaged area. Let's start with checking.
How to find a damaged thread?
To troubleshoot, you can use one of several methods:
- First you need to make a visual diagnosis. If the car glass is fogged up, then activate the CO. Fogging will remain on the damaged area of the surface after all the other threads have warmed up and the auto glass has fogged up. This self-check option is considered one of the simplest.
- Also, diagnostics of performance can be carried out using a tester - a voltmeter. To do this, you will first need to turn on the ignition and press the CO activation button. Then one probe of the tester will need to be grounded, that is, connected to the car body, and the other one will need to be wrapped in regular food foil, and then brought to the heating path.
When carrying out diagnostics, a voltage value should appear on the voltmeter display, which will be no more than five volts (this is ideal). If the voltage value is near zero or increases to twelve volts, this will indicate that a break has occurred on this track. Thus, it will be necessary to diagnose all tracks. - There is another way to check CO using the same voltmeter. In this case, you will need to connect one contact of the tester to the positive terminal of the CO, and the others will need to be moved along the track, only from the side of the negative terminal. In the place where the track is damaged, the voltage value will sharply drop to zero.
- If you do not have a voltmeter, but have an ohmmeter, then you can also check the system with such a device. In this case, the tester probes will need to be connected to the negative as well as the positive contact of the CO. Then you will need cotton wool - a small piece needs to be moistened in distillate, and then passed along the incandescent path. The moment the arrow on the tester starts moving, you will find a break (video author - Over 9000).
How to make repairs yourself?
If you are faced with a problem with the CO not working, then you don’t have to trust specialists to repair it - you can do everything yourself. There are several methods for restoring CO.
So, how to repair the system:
- For repairs, you can purchase a repair kit. As a rule, repair kits for performing this task have identical parameters and characteristics - with their help you can restore no more than 10 cm of the damaged section of the track. The repair kit includes the threads and a bottle of polymer resin. In this case, you will first need to accurately determine the damaged area; to do this, you can resort to one of the methods described above.
When the repair location has been determined, you need to turn off the CO and remove the film from the car glass. Then the surface is carefully cleaned and degreased, after which a new track is applied to the damaged area. Using a special brush, which should also be included in the kit, you need to apply the polymer resin to the surface, and when it dries, repeat this step again. After completing these steps, you will need to wait at least 24 hours, only after that the CO can be turned on. - As an option, to restore the CO’s functionality, you can purchase a special conductive paste. How to restore CO paste - one layer of it is applied to the damaged section of the track, but keep in mind that in this case you will need to grab the undamaged thread on both sides by about 2-3 cm. In this case, you will also need to wait at least 24 hours before further use CO. To dry the paste faster, you can blow the car glass with a hairdryer.
A vehicle rear window heating system is a common equipment for almost every modern car. The purpose of this functional addition is to remove ice crust or perspiration from glass in winter. If the heated rear window does not work, visibility deteriorates and the driver is deprived of the ability to rationally assess the circumstances on the road surface behind his own car. A quick repair will help restore safe driving.
Heating system design
To understand how to restore the heated rear window, it is worth first studying the principle of operation of this system. Its purpose is to eliminate fogging and prevent drying out the air in the cabin. In winter, this function is indispensable, since the icing is evenly removed from the glass and at the moment when you already need to drive, the view is 100% free.
The principle of operation of such a system in the case of a windshield is the efficiency of directed air flows of heat.
When it comes to the rear window, compact heating elements come into play, the source of which is the electrical network. Metal tracks are fixed on the glass surface from the interior side. These are numerous thin ribbons through which electricity passes, activating the process of heat generation. As a result, due to the heating of the glass, water evaporates and the surface becomes transparent within a couple of minutes.
Scheme of work
To know how to restore the heated rear window of a car and approach the repair with a high level of professionalism, study the principle of operation and the electrical wiring diagram. From the + terminal of the battery, power is sent to the ignition switch, then to the fuses and, lastly, to the controller. After this path it follows to the power contact of the relay. The vehicle body is connected to the negative terminal of the battery. Activation of the heater supplies voltage to the relay winding, then the power contacts are closed, and the relay terminals are also connected. The current flows through parallel-connected heater strips and then reaches the negative terminal through the body of the machine.
Remember, activation of the heater is only possible with the ignition key activated.
In some cases, a running motor acts as a factor predisposing to activation. This feature is due to the fact that the battery should not be discharged prematurely, and taking into account the characteristics of each car brand, the consumption volume of this system can be 10-25 A.
Sources of the problem
Since many drivers prefer to restore the heated rear window with their own hands, you need to know about repair options taking into account the source of the problem. There will be no obstacles to independently checking the functional components of the car if you have minimal skills in repairing automotive equipment.
The safety element is the first thing that should attract your attention when a breakdown is detected, since the system will not work if it is burned out. The location of this element varies depending on the car model, so at this stage you will have to turn to the vehicle service book for help. Next, remove the fuse and make sure it is working. Repair of the rear window heating will be limited to replacing the burnt out element.
A breakdown of the system relay can also lead to the heating stopping. In such a situation, installing a fresh element will also be sufficient.
Wiring
If replacing the fuse does not correct the situation, proceed to diagnosing the power supply wires. Burnout, broken fastening or fracture help stop the flow of current to the heating poles. To detect this circumstance, turn on the heating button and measure the terminal voltage with a tester. The terminals can be found at the bottom of the glass or on its sides. The lack of voltage on the wires should alert you.
Examine the entire wiring path for integrity, clean the contacts of the terminals and connections. Oxidation in these areas often leads to blocking the voltage supply. If you were unable to cope with this task yourself, an auto electrician will help you.
If the heating tapes are damaged, it may also be necessary to restore the heated rear window. To know how to do this, you must first study the peculiarities of the work process in this zone. The heating element receives voltage and then the energy follows the threads. In relation to the base, they are connected in parallel and act as current conductors. Their heating is due to a certain amount of resistance; despite the insignificant heating temperature, this is sufficient for its purpose. If one or more threads are damaged, no current flows through them, therefore, these areas do not heat up. The features of repair work in such a situation are described below.
Controls
If all the elements that you checked earlier are working properly, you should pay attention to the power button. You can determine the operation of the system by the light indicator that lights up, which makes itself known after pressing the button. If everything is activated and the corresponding indicators make themselves felt, but the glass is not heated, the working contacts of the toggle switch are likely to wear out or burn, so energy is not supplied. Repairing a heated rear window of a car only requires replacing the button.
Imported cars
In the case of imported cars, do-it-yourself rear window heating repair will not be limited to diagnosing the standard heating system, since the rear view mirrors are also equipped with heating. Activation of the heated glass of the stern leads to parallel activation of the heated mirrors. If the system does not work on both zones, it is most likely that you are dealing with the cause discussed in the first paragraph - a fuse or relay.
It is important to determine which fuses are associated with the glass, because there are several of them. It would be a good idea to diagnose the electronic board, which often wears out due to soldered contacts and broken tracks.
Phased renovation
The first thing you need to do is diagnose it and purchase a repair kit. There may be several options for a repair kit, and the repair technology in each case is discussed below.
In addition to visual diagnostics of the condition of the threads, there are several more methods that are more reliable and effective:
- Visual diagnostics require activating the heater when the rear window is foggy. Where the threads are broken, the surface will warm up almost instantly, while in other areas visibility will be problematic.
- Using a voltmeter requires activating the ignition and then turning on the heating system. One probe should lie on the vehicle ground, and the second near the center of the heating tape. First wrap the second probe with foil. The break will be localized in the area where the voltage rises to 12 V or drops to zero. Ideally, this parameter should not exceed 5 V.
- The second method of using a voltmeter involves fixing one probe to the positive terminal of the heater, and the second one must be moved along the negative terminal strip. The problem area will be where the voltage is zero.
- Using the ohmmeter requires activation of the kilo mode. The device must be analog, with an arrow. The probes should be located near the system terminals, which are located in opposite directions from each other. Use distilled water to wet the cotton wool, which must be smoothly passed over the tape. As soon as the needle of the device moves, you will be able to detect the cliff area.
Repair with conductive glue
Repair of the rear window heating threads can be carried out using conductive adhesive. It is designed for temperatures from -60 to +100 degrees. You should not choose kits with glue, which cost 150-200 rubles. Often they do not last long or may not be effective at all. A cost of 300-400 rubles would be optimal for such a set.
Work order:
- Please read the instructions included with the kit. You should have a clear understanding of the options for applying the composition and the speed of its complete drying.
- Prepare the problem surface. Soak a rag in the alcohol solution and wipe the area.
- Lightly sand the edges in the break area with grade-grade sandpaper. It is enough to simply remove plaque and carbon deposits in two movements.
- Use tape to cover the strips along the thickness of the sides. It should not overlap the thread, but also avoid going too far away from the tape. Focus specifically on the width of the thread.
- Proceed to apply conductive glue to the prepared area using a brush or syringe. The instructions will tell you how many layers to apply. The overlap on the working areas of the tape should be 1 cm to the left and right.
- Remove the tape and wait until the composition dries completely. This will not happen before 24 hours.
- Check the functionality of the system after drying.
Among the popular and reliable manufacturers of repair kits, which include threads, it is worth highlighting Quick and Permatex. Such options are suitable for repairing even large areas, even spruce we are talking about 10 cm. The equipment includes heating tapes, polymer resin in the form of a spray can and stencils.
Heater repair involves the following steps:
- determine the rupture zone and prepare a thread of the appropriate size;
- remove the protective film and use resin to fix the thread in the required area;
- After complete drying, repeat the manipulations and check the result after 2 days.
Alternative method
Traditional methods are also suitable for restoring threads. The only difference between them is the material used:
- Wood shavings combined with paint. The first material can be obtained from a bar of copper and brass, which must be processed with files. Choose a paint that matches the color of the heating tapes. Mix the ingredients in equal proportions until you reach the consistency of a soft dough. Use masking tape or tape to create a stencil. Paste the stencil and activate the heating. Contact can be determined by a characteristic hissing sound. Apply the mixture using a stencil. This method eliminates the need to wait a day. You can operate the car immediately after the manipulations.
- Soldering of the broken area is carried out using zinc chloride. Give preference to solder with a minimum tin content - POSS-4-6 or POS-18. A copper or silver core is suitable for repairing a large section of tape.
You will need
- - voltmeter;
- - low-tin solder and zinc chloride;
- - graphite powder, iron filings, nitro varnish, epoxy;
- - silver filings and nitro glue;
- - solution of copper sulfate, cloth, long copper wire;
- - electrically conductive glue
Instructions
Look for damage to the heating filaments using a voltmeter. To do this, connect one contact of the device to the current-carrying busbar, and smoothly drive the other along the idle strip. Another method for finding a broken thread: turn on the heating on foggy glass. In this case, the entire glass will quickly sweat, except for the damaged area. This method is simpler than the previous one, but is not accurate and does not always work.
Regardless of the chosen repair method, first remove the varnish from the damaged area until a metallic sheen appears. It is more convenient to do this with bent wire. Degrease in any way. Having soldering skills, solder the damaged area with soft low-tin solder such as POS-18 or POSS-4-6. Use zinc chloride as a flux. If there is damage over an extended area, solder a thin copper or silver core from a suitable piece of wire.
To restore using another method, coat the damaged area with a mixture of graphite powder and a small amount of epoxy glue (resin). To make the work better, install a strong magnet on the back of the glass, and sprinkle small metal filings in place of the area to be restored. They will restore thread contact. After repair, treat the damaged area with nitro varnish. Remove the magnet after the varnish has completely dried. When applying sawdust, try to get it as accurately as possible onto the strip of conductor, and not onto the entire surface opposite the magnet. This will help make the repair site invisible.
For the third method, take silver filings. Prepare them by grinding off the contact alloy of the unnecessary power relay with a file. Pour sawdust into the fold of a sheet of paper and add a drop of nitro glue. Using the end of a knife, quickly roll the sawdust into a cylinder with a diameter of 1 mm and a length of 2-3 mm. Apply it to the damaged area and crush it, pressing the sawdust firmly. Remove any excess.
Another method is perfect for restoring a damaged area or the entire heating thread. Prepare a solution of copper sulfate consisting of 6 parts water, two parts powdered sulfate and one part battery electrolyte. Mix thoroughly. Take a thick, long copper wire that extends from the positive terminal of the battery to the glass with threads. Wrap a piece of fabric 1-2 cm wide and 10-15 cm long around the end of the wire and secure it in any way.
After connecting the other end of the wire to the positive terminal of the battery, soak the wound cloth in the prepared solution. Begin vigorously rubbing the tear area for 1-2 minutes. In this case, copper will begin to deposit around the undamaged thread. A copper coating will look like patterns on frosted glass. When restoring the entire thread, start from the place where it is connected to the side live parts. This method is cheap, accessible, and has a high durability of the restored area. On the other hand, it is quite long.
To use a more modern restoration method, purchase a special electrically conductive glue. When purchasing, consult the seller. To restore the thread, use the stencil included with the product. Using a soft brush, apply glue through a stencil to the damaged area and dry for 10-15 minutes.
In winter, on cars in which the air conditioning does not work well, the rear window defroster is a real salvation. Driving a car without being able to assess the situation behind you is extremely irresponsible, and it is not recommended to go to parking areas with ice on the rear window. Some drivers use a scraper to remove ice, but most car models have a rear window defogger that can eliminate the ice problem.
The rear window defroster is a very simple device that consists of a series of horizontal lines of electrically conductive material applied directly to the glass. Near the side edges of the glass, vertical conductor lines approach the threads, through which the current flows to the electrically conductive material. The simple design of the rear window heater suggests that there are not many reasons that can lead to its failure. Below we present the main reasons why the device may not work, as well as methods for repairing the rear window defroster.
One of the most common malfunctions of this car component is a broken thread. Thin electrically conductive threads only need to be slightly touched for a rupture to occur, and this will lead to the rear window defroster no longer performing its intended functions. Most often, problem areas are diagnosed visually.
If you cannot detect visible breaks in the rear window defroster filaments, you can use diagnostic tools to troubleshoot the problem. Get a multimeter and use it to measure the voltage in all sections of each thread. For example, 5 conditional control points are taken on each thread. The negative probe of the multimeter is connected to ground, and the positive probe is connected to the test points of each thread. Moving the measuring probe from one end of the thread to the other, a voltage drop from 12 to 0 Volts should be observed on the device. If at one of the control points the voltage is higher or lower than normal, then you should take a closer look at this area, since there is an open circuit there. 
Attention: Apply a sharp probe to the heater filaments carefully so as not to cause further damage.
Repair. A car enthusiast can easily fix such a malfunction on his own. Automotive stores sell a special kit designed to restore the rear window defogger pattern. The kit includes a stencil, conductive glue and a brush. The stencil is glued to both sides of the damaged area, after which conductive glue is applied to the problem area. Next, you need to wait until the composition dries (about 30 minutes) and remove the stencil. 
Rear window defroster fuse blown
If any electrical device on your car stops working, the first thing you need to do is... Fuse failure can be caused by a temporary surge in current in the vehicle's on-board circuit or a more serious malfunction.
Repair. First, try simply changing the fuse and using the device normally. If the problem persists and the element fails again, identify and fix it.
The rear window defroster may stop working properly due to oxidation of the contact directly bonded to the glass. To detect this malfunction, you need to measure the voltage of the supply wire and make sure that it exceeds 11 Volts.
Repair. If the measurement results in a value less than 11 Volts, it is necessary to clean the contact from any oxidation that has formed. To clean the contact, you can use fine-grain sandpaper or a special rust remover.
Other malfunctions of the rear window defroster
If all the diagnostic procedures described above have been carried out, but the problem is not found, it means that the rear window defroster is not working due to a broken wiring or failure of the power button. It is recommended to first look into possible problems in the button, and if they are not found, you will have to diagnose broken wires.
