Car rear window heater: how the defroster works and what problems may occur
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Without your handy rear window heater, you may have trouble seeing behind your car on those dangerously frosty mornings. This can severely affect your visibility and lead to preventable road accidents if ignored.
What does the rear window defroster do?
You may have noticed the thin black or coloured lines running across your car’s rear window. These parallel lines are actually electrical heat conductors that are built into the glass. The rear window heating elements also include the car window heater relay that prevents overheating, the wiring harness, and the switch.
When the rear window heater, a.k.a. the defroster or defogger, is switched on, it sends an electrical current to the metal grid lines, heating them up. This heat causes any ice, snow and frost on the window glass to melt away, ensuring that you have a clear view of what’s behind you. It also prevents the window from fogging up while you drive, which is particularly useful on a frosty morning.
To activate the heating system, simply push the rear heater button on the centre console or the dashboard. This button usually has a rear window heater symbol on it, which usually looks like a straight rectangular panel with three arrows pointing upwards.
Will the heat affect the rear wipers?
The heated rear window should not adversely affect the rear windscreen wipers. The heat from the grid will actually help the wipers by deicing or defrosting the wiper blades, allowing them to move freely.
Why is the heated rear window not working?
The heated rear window may not be reaching a warm enough temperature due to a damaged grid or worn electrical components. For example, people often make the mistake of scraping off the rear window sticker or tint film with a metal scraper, accidentally damaging the grid lines in the process.
It could also be caused by a short circuit or a blown fuse. Short circuits can occur when dirt or moisture gets into the wiring and connections causing corrosion and disrupting the flow of current, or when the wires are worn or damaged. Replace damaged wires and clean dirty connections using a special contact cleaner.
Check the defroster’s fuse in the fuse box to determine if this is the cause. Thankfully, this issue can be easily and cheaply resolved by buying a new car fuse and replacing the old one.
How do I fix my rear window defroster?
How you fix it will depend on the nature of the problem itself. As mentioned above, there are a number of possible causes which will require a proper diagnosis. The first place to start is generally the fuse as this is the most common and the easiest to resolve.
Once the fuse has been ruled out, you can go ahead and check the wiring and electrical connections, the relay and the heater switch. Replace any defective car parts along the way. Physical damage to the grid conductors in the window may mean that you have to replace the glass pane. However, in some cases, you can repair the damage using a grid repair kit.
If your rear window heater is not automatic or the automatic function isn’t working, you’ll need to remember to switch it off yourself once it has done its job. Otherwise, it will drain the electrical power supplied by the car battery and alternator. If your battery needs replacing, find out where to buy a car battery online.
