When your car heater isn't working it can be extremely frustrating. When you're up early for work on a frosty cold winter morning, the last thing you want to deal with is a car that is as cold as the outside for the entire trip. It's inconvenient, distracting, and it can even be a danger. If the heat in your vehicle isn't working and your windshield begins to frost up, then you could be in danger of an accident if it starts happening while you're driving down the road. For that reason, it's worth knowing why your heater stopped working in the first place and what you can do to get the warm air blowing again.
As it happens there are a handful of reasons that your car heater could not be working even though your car seems to be working fine otherwise. Let's take a look at some of the most common reasons why your heat could fail and then what you can do about them.
Reasons Your Car Heater is Blowing Cold Air
The engine in your vehicle runs at a very high temperature once you've got your car running for a while. It's the heat from the engine that is actually diverted to the inside of the cabin to keep you warm. The coolant goes from your radiator through the engine and absorbs some of that heat. It then circulates through the heater core where, when you turn the heater on, fans blow that warm air into the cabin to help keep you toasty and also help keep your windshield defrosted when that's the problem as well.
If your car is running normally, then your engine is producing heat. If the heat can’t get to the cabin of your vehicle then there's a problem somewhere in that system that circulates the heat from the radiator through to the engine and back again that's preventing this from happening. A number of parts in the system can fail on you for different reasons.
Even if the heater in your car is technically working properly, if the fan is not working, you're not going to feel it. In order for the heat to actually circulate it needs to have that fan blowing on it to help push it into the cabin of your vehicle. Otherwise, the heat kind of sits still and will radiate a small amount from your vents but not nearly enough to make it effective.
When you turn your heat on, if you don't hear the fan running at all even if you try to crank the heat up, then that's a good sign your fan is the source of the problem here. Every heater should have a few different intensity levels and the fan icon on your dashboard or heater control will indicate how powerful the fan should be running to blow the heat into your vehicle. If it's cranked all the way up, and you're not feeling any air or hearing the sound of a fan blowing then it's almost guaranteed this is the problem.
If this is the case, you want to check the fuse for your fan, or blower motor, to make sure it isn't blown. You'll have to check your owner's manual to find out where exactly that is, or Google the make and model of your vehicle to track down the right fuse. If that is the problem, then a simple fuse replacement will get it fixed for you and that's only going to cost you a few dollars. However, if the fuse is not the issue then your fan itself may be dead. If you have an older vehicle, this is definitely a possibility.
If your blower motor has failed, getting it repaired will probably cost you between $300 and $400.
Although it doesn't seem like a coolant should have anything to do with the heater in your vehicle, the fact is that coolant is responsible for keeping things cool and warm, as paradoxical as it sounds. Coolant works by taking the heat away from your engine. In doing so it becomes very hot itself. Before it recirculates to the radiator and cools down again, your car makes use of that excess heat by running it through your heater core. That way, if you need to heat up your cabin you can do so without having to expend any more energy. It's actually a very efficient system when it works properly.
When things are not working, that can definitely cause your heater to not work the way you expect it to. If you're suffering from low coolant, it's not going to be able to circulate through the entire system properly in a way that transfers heat from the engine to the cabin of your car. Likewise, if there is air in the system it will be inefficient at transmitting heat as well.
Another issue when it comes to your coolant could be the quality of the liquid. Over time, coolant will degrade if it becomes contaminated with rust or other debris. Dirty coolant is not able to do its job properly and that can also prevent your heater from working the way you need it to.
You can inspect the coolant levels and quality in your vehicle fairly easily to see if that's the nature of the problem. Your coolant levels can be inspected visually just by popping the hood and looking at the reservoir. There should be a minimum and maximum fill line and the coolant level should be visible in between. If it's low, then you know you need to add more. Just remember to add the same kind of coolant you're already using, you never want to mix coolant types such as green antifreeze and orange antifreeze, because that's going to create a jelly-like substance which will make it even less efficient and require a full flush to clean out.
If your coolant is contaminated in some way, if the colour has become muddy and dark, or you can actually see particles floating in it, then you're going to need a coolant flush to clean the lines out and replace it with new, clean fluid.
The thermostat in your car is a fairly simple piece of technology but if it malfunctions, it can have some lasting ramifications. In order for your car to work properly the thermostat is either going to be in the open position or the closed position. When your thermostat is closed it prevents coolant from getting to the engine. This is important sometimes, such as when your engine is actually cold and just getting started.
Your engine needs to get up to operating temperature because even though a cold engine may not be as damaging as an overheating engine, it's also inefficient to work at low temperatures. Once your engine is at the temperature it needs to be, your thermostat will open to allow coolant through to prevent it from overheating. If it gets too cold again, the thermostat closes to prevent more coolant from flowing through. There's not a lot to it and it seems very simple. However, thermostats are notorious for getting stuck in either the open or closed position.
If your thermostat is stuck in the closed position, then the coolant can't flow, and that means it can't reach your heater. Sometimes a simple cleaning of the thermostat to get rid of any debris that may be clogging it to prevent it from moving properly is all you need to do. If your thermostat needs to be replaced that is also an option but it can be a pricey job. A mechanic may charge you between $200 and $300 to get your thermostat replaced. Of course, if you're inclined to do do-it-yourself repairs you can save a lot of money on this job if you know what you're doing. Some thermostats on a site like AutoZone can be as cheap as $12. At the higher end they can get to $150. Still, that's a savings if you are able to handle this repair job on your own.
A rare but not unheard-of reason for your heater to not work properly is that the control buttons that operate it have failed on you. Whether that's an actual push button on your dashboard or a dial that you turn, if the mechanism itself fails then it will be unable to transmit the signal to your heater that you actually want heat to work. So, your heater may still be functioning perfectly fine, it's just that you no longer have the ability to turn it on and off. If you don't feel any kind of resistance when you turn the knob for your heater, or it literally comes off in your hand, then this is definitely a sign that you have a problem here.
Heater Core Problems
The part of your car's heater that actually is responsible for producing the heat that you're going to enjoy on a cold day is called the heater core. The coolant that leaves your engine travels through a hose into the heater core. When you're not using the heat, it continues through the heater core, through another hose and back to your radiator. If you do need to use the heat, then a fan will blow the hot air from the heater core into the cabin of your vehicle. Overall, that's a fairly simple design.
If you have a problem with your heater core there are a few signs that you could be on the lookout for to let you know that this is the reason why the heat is not working in your vehicle.
Sweet Smell: Coolant has a very distinct and sweet odour. If the heater core in your vehicle isn't working properly, and there is a leak in the system, when you attempt to turn on the heat the fan might just blow that smell into the cabin of your vehicle. It's also possible you would notice the coolant itself leaking into your vehicle.
Visible Coolant: Aside from the smell of the coolant coming from your heater core, you may notice it leaking in a couple of different ways. It's possible it will run down the inside of your cabin either from the vents, or from behind your dashboard possibly down by your feet along the walls inside your vehicle. You may also notice it when you turn on the defroster and a misty spray blows up over your windshield. It will leave a sticky, fog-like coating on your windshield that's hard to wipe off. That's coolant that's become aerosolized because there's a leak inside the heater core.
Overheating Engine: Obviously if you have a coolant leak, it's not going to be able to keep your engine at the temperature it needs to be. If you don't have heat in the cabin of your vehicle but your engine is overheating, then there's no doubt about it you have a coolant leak somewhere.
As we said earlier, low coolant levels are a potential cause for your heater not working, so this leak could be in the heater core itself, or it could be somewhere else in the system. Whatever the case, an overheating engine can cause some severe damage and end up costing you thousands of dollars in repairs so you're going to want to get this one fixed up as soon as possible.
The Bottom Line
As we've seen there are a number of reasons why the heat may not be working properly in your vehicle. Getting it fixed definitely depends on properly diagnosing the problem, so you know where to go to address the issue. Of course, you don't want to spend hundreds of dollars on a new thermostat or a replacement heater core but engaging in some routine maintenance can help prevent a lot of these problems.
Make sure you keep your coolant levels topped up and flush the system anytime you notice that the coolant has become contaminated in any way. This will prevent heater problems in the future, and also prevent any serious damage to your engine from overheating which can occur as well. Remember it's always better to pay a couple hundred dollars for a small repair if it helps you prevent spending a few thousand dollars for a major engine repair further down the road.