How this system works:
The front defroster uses the same blower motor, fan and venting system that the heating and air conditioning system use. Air passes through the heater core and then dry air that has been run through the air-conditioning evaporator is added to help remove the moisture from the windshield. All of this air is sent out through the defroster vents on the top of the dashboard. The hot air removes the any snow or ice while the dry air helps eliminate the humidity and fog.
On most vehicles, the rear window has tiny lines going through it, which are electrical wires. These wires heat up as current flows through them. The heat displaces the condensation on the window. These wires produce a very low heat factor so there is no danger of anyone getting burned if they touch the window.
Common reasons for this to happen:
- Buttons Stuck: In some cases a button or knob for the heating controls becomes stuck. Moving them back and forth until it moves into the defroster position may solve this problem.
- Blocked fresh air intake: The fresh air intake is at the base of the windshield. It draws in fresh air, which helps the defroster function. If leaves or other debris are blocking the air intake it will affect the defroster.
- Vent Issues: If the vents on the dashboard are clogged, this will prevent the air from reaching the windshield. A quick vacuuming of the vents may fix the issue, if not the clog may be deeper in the system and require a professional.
- Low Anti-Freeze: The heater core depends on hot antifreeze moving through it to heat the inside of the car. If the vehicle is low on antifreeze, it can affect the heating and defrosting systems. Anti-freeze should be checked and replaced on a regular schedule.
- Malfunctioning Thermostat: The thermostat in a car works like a shut-off valve between the radiator and the engine. It remains closed when the car is first started to build up heat. Once the engine is warm the thermostat opens up to circulate anti-freeze to prevent the engine from overheating. If the thermostat is stuck open, the engine doesn’t warm up, so the defroster will not have the warm air it needs to function properly.
- Bad Heater Core: The heater core is basically a mini radiator that is located behind your dashboard. It is the heart of the heating system and essential to the defrosting system. There are a number of things that can cause a heating core to go bad, it can become clogged up due to contaminants in the anti-freeze, hoses can come loose or broken and control valves can become stuck. A bad heater core will result in no heat, which means a non-functioning defroster.
- Bad Blower: The heating and defrosting system rely on an electric blower motor to move the hot air into the cabin of the car and through the defroster vents. If the blower motor is malfunctioning, the defroster will not work. Issues can range from a blown fuse to a bad blower speed controller. The blower motor itself can also go bad and need replacement.
- Broken Grid: The most common issue with a rear defroster is physical damage to the heating grid running through the rear window. Damage can be caused by objects rubbing across the glass, which can break some of the grid wires. If the grid is damaged, it opens the circuit. The defroster will not function from the point of the break forward.
- Broken Tabs: There are tabs on the sides of the rear defroster, which connect the defroster to the window and the circuit. One of these tabs acts as the positive and the other is the ground. If one of these comes off or fails, the defroster will no longer work.
- Old Age: As defrosters age they can lose their conductivity which reduces their ability to conduct an electrical current. Repeated cleaning, the sun and objects rubbing over the grid will eventually wear the grid down and at some point may break it, rendering the defroster inoperable.
- Window Tinting Damaged Defroster Lines: When window tinting is applied it comes into contact with the defroster grid and can bond to the heating elements. It is possible that defroster lines can be broken during installation or removal of a window tint.
What to expect:
A top-rated mobile mechanic will come to your home or office to determine the source and cause of the defroster system issue, and will then provide a detailed inspection report that includes the scope and cost of the necessary repairs.
How important is this service?
A totally or partially defrosted windshield or rear window can seriously affect your visibility, leading to a very dangerous driving situation. Any issues with the defrosting system should be repaired immediately.