Introduction:
The windows in the car are of course mainly there to provide good visibility. In addition, the windows also have a protective function. The windscreen must not completely block the view when an object (such as a small stone) hits and damages it. The side windows must not splinter when they break, as this could cause injuries.
All windows also have standard UV protection. The windows are therefore slightly green or blue tinted, which blocks UV radiation and thus also heat. The UV protection provides a tint of approximately 20% and can keep out temperatures of up to 20°C.
This page describes the different types of windows and their applications.
Windscreen:
In passenger cars, windscreens are now always bonded in place. In older passenger cars and some modern trucks, the window is clamped in rubber seals in the bodywork recesses. The bonded windows (both the windscreen and the rear window) provide additional rigidity to the body. Due to the special windscreen adhesive, the windows essentially form one unit with the bodywork.
In the past, windscreens were made of toughened glass. When an object from outside (such as a small stone) hit the windscreen, there was a good chance that the entire window would shatter. This created many small fractures across the entire window surface, completely obstructing the view (see the image).
Today’s windscreens are made of laminated glass. The advantage is that an impact causes a chip or a crack. The view is never completely blocked as with toughened glass, and with minor damage the chances of repairing the windscreen are very high. Laminated glass consists of two layers with a thin layer of transparent film in between. The thickness of the inner and outer layers of the window are both 3 millimetres. In case of damage, small hairline cracks occur in the outer layer of the window.
Repairing windscreen damage:
In the image below you can see damage to a laminated window. A small stone has hit it, causing tiny hairline cracks in the outer layer of the glass. Because light now reflects off the cracks, these parts appear darker. Damage such as in the image below can easily be repaired up to the size of a 10 Eurocent coin.
During repair, special repair fluid / resin is pressed into the cracks under pressure. Because the space between the cracks is now filled, the light no longer reflects off the 2 separated parts of the glass. In this way the damage can be made almost invisible. The risk of the windscreen cracking further is also minimised. A windscreen repair is never completely invisible, because the point of impact will always remain visible as a stone chip mark. However, by polishing, the impact point can be reduced as much as possible.
Replacing the windscreen:
If the damage or cracks are too large, the windscreen can be replaced. According to the MOT inspection requirements, damage in the field of vision smaller than 20mm is allowed. If the damage is larger, or the cracks branch in various directions, there is a good chance the windscreen will fail the inspection. The windscreen must then be replaced.
When replacing the windscreen, the old window is cut out. The adhesive is cut out of the recesses using special knives or cutting wire. The windscreen is then lifted out and the old adhesive residues are removed. Any damage caused during removal must be repaired to prevent rust in the future. The recesses must also be cleaned and degreased. After that, the adhesive layer is usually applied to the windscreen. Sometimes it is applied directly to the car first. After applying the adhesive, the windscreen is placed in position as quickly as possible. The top of the window is fixed to the roof with tape or special suction cups so it cannot slide down before the adhesive cures.
It takes some time for the adhesive to fully cure, so it is advised not to slam the doors when the windows are closed (because of the air pressure in the car) and to leave the car standing for a while (at least 2 hours).
If the windscreen is not installed correctly, the following faults may occur:
- Leaks occur because the window adhesive was applied incorrectly
- A whistling noise can be heard while driving (the windscreen is probably fitted too high or too low)
- A crack appears in the window again after a very short time (the window was installed under too much stress)
If these problems occur, you can contact the company that replaced the window to claim under warranty.
Damage to the other car windows:
The side windows and the rear window of the car are made of toughened glass. When they break, the window must shatter into very small pellets. These pellets must not be sharp, as the occupants could otherwise suffer additional injuries in the event of a collision. The occupants must also be able to easily smash the window if the car ends up in water, for example. In the image below you can see what a side or rear window looks like after it has been smashed. The parts that are still present will easily crumble away when gently pushed. Of course, there is still a risk of injury when handling the glass, but this is much safer than large glass shards.
The side windows can be either clamped or bonded. Windows at the rear passengers that cannot be opened (such as in a 3-door car) are often bonded. In a 5-door car, the rear windows are often partly clamped in the rubber seals (small window) and partly mounted on the window regulator (so that they can be opened and closed). The latter also applies to the front doors. More information about the attachment to the window regulator can be found on the window regulator page.
Rear window:
The rear window contains visible wires that heat up when current flows through them. Any moisture on the rear window will quickly evaporate when the rear window heating is switched on. The full onboard voltage of 12 volts is applied to the rear window heating wires. The heating requires approximately 10 to 15 amps to function.
If one or more wires are damaged, part of the heating may stop working. When the rear window heating is switched on, a moist patch will remain along the affected wire. This is along the entire length of the wire. When the wire is broken, no current can flow through it, so it will no longer heat up. The most common cause of a broken wire is an object rubbing against it from the luggage in the boot.
A voltmeter can be used to measure the voltage on the wires. The positive probe of the voltmeter can be held on the wire and the negative probe must be held on the vehicle ground. With the voltmeter, you can determine where the wire break is located.
Repair kits are available that allow you to reconnect the broken wires using a conductive liquid. The conductive liquid can be brushed on to the break using a small brush. Once the liquid has dried, the rear window heating will function again. However, the repair spot will remain visible.
Nowadays, antennas are increasingly integrated into the rear window. By placing antennas in multiple locations (sometimes also in the rear side windows), optimum radio reception is always obtained. The radio will then select the strongest signal.
Windscreen heating and demisting:
In winter, the windows can fog up from the inside. The windscreen demisting system, which is mandatory in every car, blows warm air against the window to evaporate the moisture. The demisting only works once the coolant has warmed up. Every car has rear window heating on the rear window. The rear window contains small heating elements (these are the horizontal lines you can see) which heat up when current flows through them. Every car has a button for the rear window heating, and cars with automatic climate control also have a button for the windscreen demisting. In cars without automatic climate control, the rotary knobs must be set to the windscreen and to warm.
The windscreen demisting works by blowing warm air through the vent (across the width of the dashboard) against the windscreen. The side windows are also demisted, via the smaller vents in the dashboard that cannot be adjusted (see image below). These vents direct the air at a specific angle so that the entire glass surface is cleared of condensation.
If the windscreen demisting does not work (for example because the heater fan is defective, or the flaps in the heater unit do not move), this is a reason for MOT failure. During the MOT, the airflow along the windscreen is always checked. If the windscreen keeps misting up, there is often a moisture problem (water leakage along door seals, the window regulator or the door membrane), or the cabin filter is clogged with damp leaves.
In some luxury cars, the windscreen is also equipped with heating wires. These heating wires usually run vertically across the windscreen and are barely visible. The advantage is that the coolant does not first need to be warmed up before the air-based demisting can do its job, and any frozen wiper blades will also defrost.
Double glazing:
Sometimes double glazing is also used in cars. This is often in vehicles from the higher-end segment. Usually this is for extra security. Two windows, each 3mm thick, are fitted against each other. Between the panes is a special film to prevent moisture and condensation forming between them. The advantages are that outside noise is greatly reduced and that double glazing provides strong thermal insulation. The disadvantages are that the entire door has to be modified by the manufacturer: the window regulator, the window motor and the door hinges must be made heavier, and the door panel must be adapted. Double glazing also cannot easily be broken in an emergency situation, for example when the car ends up in water.
Rain / Light sensor:
The rain / light sensor is mounted behind the interior mirror in luxury cars. This sensor registers raindrops and light intensity. The functions of the wipers and the vehicle lighting are controlled based on these sensor values. More information about the RLS will follow later.
Tinting / Blacking out the windows:
As standard, car windows are tinted up to 20%. This is often recognisable by a greenish / bluish sheen. The standard tint has a heat-repellent effect, because it partly blocks UV radiation. With tinted windows, the temperature can drop by up to 20°C. Windows can also be additionally tinted. This is usually done by applying film. This film is often dark grey in colour and enhances the UV-blocking effect. Windows are also often tinted for cosmetic reasons; a car with tinted windows often looks neat and sporty.
There are limits to additional tinting of the car:
- The windscreen and the front side windows may be fitted with film, provided that the light transmission is at least 55%.
- The side windows for the rear passengers, any side windows at the boot in an estate car and the rear window may be tinted without a maximum value. These windows may even be covered with black film that does not let any light through.