If you have ever had to get ready for a drive on a cold winter morning then you have probably experienced what happens after you scrape all that snow and ice off the outside of your car and then hop inside to try to get warm. Your front windshield is probably all fogged up and you'll need to sit there with the defroster running for a good 5 minutes or so before it can clear up enough so that you can safely pull out of your driveway and head out on the road.
The defroster at the front of your car uses the same system that your air conditioner and heater use to either keep you cool or warm as needed. That means the same blower motor, the same vent system and the same fan. The only real difference between your defroster and your heater is the direction that the air is going to be blowing when you turn it on.
How Does a Defroster Work?
When you turn your defroster on, air flows through your heater core while dry air that has had the moisture stripped away by your air conditioning evaporator is included in the mix to help break down the crystals or condensation that have formed on the inside of your windshield. The combination of hot air and dry air is able to eliminate ice, fog, and condensation in general.
The rear defroster in your vehicle works a little bit differently. You'll notice if you take a look at the rear window of most vehicles that there is a very fine grid of electrical wires that cross the length of the window. When you turn on the rear defroster a current goes through these wires that warms the window. That in turn causes the condensation on the window to evaporate while melting any ice or snow that may be in the way. The heat they produce is extremely low, you'd never burn yourself on it for instance, but it is warm enough that it can affect freezing water.
Unfortunately, sometimes your car can suffer problems with either the front or the rear defroster that prevents them from working the way you need them to. This can actually render your car completely undrivable in some circumstances. If the situation is bad enough you'll have a layer of ice covering your windshield that needs to be removed. Depending on weather conditions even if you scrape this off by hand it may form again as a natural result of you being in the cabin of your vehicle and breathing out warm air that condenses on the windshield. It can be extremely frustrating trying to solve this problem when the defroster isn't working. Let's take a look at some of the reasons your defroster might not work, as well as what you may be able to do about it.
Causes for Your Defroster Not Working
When you turn your defroster on and you find that nothing's happening there are a handful of reasons that you can look into to figure out what's going on. These are the most common ones you're likely to encounter.
Low Coolant: Coolant in your vehicle works by pulling heat away from your engine. The coolant travels from your radiator into your engine where it absorbs the heat and then heads back to the radiator again. Along the way it's going to pass through the heater core which is where the heat that blows into the cabin of your vehicle comes from. If you've got low coolant levels, then it won't be able to properly transmit the heat that is absorbed from the engine to the air that blows into the cabin of your vehicle.
Broken Switch: Sometimes the most obvious answer is also the right one. If the button that you press to turn on your defroster isn't working, then the defroster isn't going to work either. Depending on how you activate your defroster, sometimes it's a knob to turn, sometimes it's a button you press, but regardless of what makes it function if that control mechanism has broken or gotten stuck in some way then you may not be able to get your defroster to turn on.
Getting this repaired in your vehicle could be fairly cheap if you can find the right part yourself to replace the switch, button, or Knob that controls your defroster. If you need to special order the part it may end up being a fairly costly repair job even though it seems like it should be a quick and easy one, sometimes costing you several hundred dollars depending on the make and model of your vehicle.
Clogged Vents: It's possible that the vents in your vehicle could become clogged if they haven't been cleaned. Dust, dirt and other debris can build up enough that the flow of air is greatly reduced and very little is actually able to come out when you turn your defroster on. You can typically fix this with the standard vacuum that you might use to clean out your car. However, if you have something stuck deeper in the lines it may take a mechanic to get the situation fixed for you.
Bad Blower Motor: The electric blower motor in your heater is what allows the air to actually blow out into the cabin of your vehicle. If this fails on you then your defroster won't have any air blowing out of it, nor will your heater if you try to turn that on.
Getting the blower motor replaced in your car could cost you anywhere between about $200 to as much as $500 or more. Again, the make and model of your vehicle has a great impact on just how much you're going to have to pay to get your blower motor fixed. That said, if the blower motor itself is still working but it was a fuse that blew, you can actually buy new fuses for your vehicle for around $5 a piece. If you can look up where the fuses are located in your owner's manual or just Google the make and model of your vehicle, you could potentially swap the fuse out yourself and get the blower motor working again for very little money.
Bad Heater Core: The heater core is what the hot coolant will pass through on its way back to the radiator. It's located behind your dashboard and it is like a small version of a radiator itself, able to absorb the heat from the coolant that has just come from your engine. if there's any kind of contamination in your coolant as it passes through the heater core, that could potentially clog the core so that it no longer works properly. As well the hoses that bring the coolant in and out of the heater core can wear out or break causing it to fail.
Replacing the heater core in your vehicle is not the easiest repair job to get done. As a result, it tends to be a little more expensive than you might think. The cost of replacing the heater core can be anywhere from about $550 to $950. This very much depends on the make and model of your vehicle. Some higher-end and rare vehicles tend to be much more expensive to repair when it comes to a job like this.
Bad Fresh Air Intake: Right near the base of your windshield you will see the fresh air intake. This pulls air in so that it can be recirculated through your defroster. The fresh air intake is easily prone to blockages, things like dead leaves and other debris can build up and clog the vents so that limited air or no air is able to pass through. Fortunately getting this cleaned is fairly easy and should only take you a few moments.
Bad Thermostat: Your thermostat has an open position and a closed position. When you first start your car, the thermostat should be closed which prevents the flow of coolant towards the engine. It will stay closed until your engine gets up to temperature at which point it will open allowing the coolant to flow through and maintain the proper operating temperature that your car needs. However, if the thermostat isn't working the way it's supposed to it can get stuck in either the open or the closed position.
In the closed position that means no coolant is going to be flowing into your engine which in turn means it's not going to be able to get to the heater core to allow you to turn your defroster on. Of course, the bigger worry here is that your engine is going to overheat.
If your thermostat is stuck in the open position, then coolant will be flowing from your radiator to your engine from the moment you turn your vehicle on. That means your engine will not actually be able to get up to temperature, and you may not have enough heat being generated to operate your defroster in a way that allows it to be effective.
If you need to replace the thermostat in your car it's probably going to cost you between $200 and $250 to get this job done.
Can You Repair a Rear Window Defroster?
if you go to a mechanic to get your rear window defroster repaired they will be able to get the job done for you but it's going to cost you several hundred dollars, potentially upwards of $400 or more. The difference between your rear defroster and your front defroster is that your rear window defroster is actually a grid that has been painted on to the glass of your car. If any of the lines in that grid get damaged it can cause the defroster to not work properly and severely limit your ability to defrost your rear window.
If you're looking to get your rear defroster fixed but you don't want to spend all the money associated with getting it repaired by a mechanic there are actually kits that you can buy to do it yourself. It doesn't take a long time to do this repair job on your own and the kits that you can buy to do the repair work yourself are only going to cost you about $15 if you buy them from amazon.com. It's a pretty remarkable savings compared to what a mechanic might charge you for the same job. Just make sure you follow the instructions exactly or you could end up causing even more damage in the long run, or just perform that repair ineffectively so then it still doesn't work.
The most important thing you need to remember when doing this yourself is to follow the directions for properly cleaning your window. It needs to be absolutely, one hundred percent clean or the grid lines you are trying to place on it won't work because they can't stick to the window.
The Bottom Line
When you think of the safety features in your vehicle you probably mostly think of things like airbags and seat belts. Even your brakes qualify as an important part of your vehicle's overall Safety Systems. But the defroster is one that we often overlook and don't really put much thought into until it's not working the way it's supposed to.
When you have a defroster that's not working properly you are essentially blind behind the wheel, and that's a dangerous situation for not just you but all the other drivers on the road as well. For that reason, you want to make sure your defroster is working as well as it can be all the time. That includes both the front and the rear defroster. If you're noticing any problems with the defroster's ability to keep your windshield clear, then you're going to want to head into a mechanic as soon as you can to get the situation sorted out. The last thing you want to be doing is trying to scrape off your windshield by hand from the inside so you can see where you're going. Especially if it starts fogging up while you're in motion rather than when you're parked and have the opportunity to keep your windshield clear.