Car Heater: A Beginner’s Guide

A car heater is an important feature of your vehicle that often gets taken for granted. While it isn’t an essential component, dealing with a broken heating system is a major hassle. When it’s warm outside and you don’t need to use it, it isn’t much of a problem. But when winter comes around and your windows are fogged up and the temperature reaches low digits, you want to be sure that it’s working. There are certainly other features that are more vital, but you should never overlook your car heater. Let’s take a look at how this function works and what common problems can arise.

What Is a Car Heater?

It’s best to begin with a clear understanding of what a car heater actually is. Your vehicle’s heater serves two helpful functions. The first is fairly obvious and that’s to keep the car cabin warm and cozy. Cars can quickly get cold when the weather outside is frigid and that can be quite uncomfortable. Luckily, when it happens, you can simply turn the heater on to keep the car at a comfortable temperature.

As you might imagine, this is only really helpful for locations that tend to get cold, especially during the winter. If you live in a particularly hot area, like Los Angeles, you might not use your heater often or at all. On the other hand, a colder city like Boston or any other up north in Canada might necessitate the use of a heater during a large portion of the year. However, keeping your vehicle’s interior warm is only half of its purpose.

Arguably more important is its ability to keep your windows clear. If you’ve ever driven when it’s particularly cold outside, then you likely know that it causes your windows to get foggy. This reduces visibility and will quickly make it dangerous to drive. Your car heater comes in handy here with its defrosting capabilities. The defrost function will direct heat to your windshield, which will clear up the fog in no time.

Both functions are incredibly useful, which is why you want to make sure your heater is always working. It’s much better to have a working heater that you don’t need than a broken one you need to clear up your windows. 

How Does a Car Heater Work?

Women adjusting car temperature

A car heater doesn’t generate its own heat, unlike electric heaters. Driving your car naturally creates heat in your engine. The heat is transferred out through your exhaust system or cooled via your vehicle’s cooling system. To extract the heat from the engine, the coolant circulates around the cylinders and other hot components and absorbs the excess heat.

This warmed coolant mixture can then be transferred to your car’s heater core. From here, a fan blowing directly through the heater core will direct the hot air into your vehicle’s air vents to warm up the cabin. Your car heater is basically just a system that redirects heat from your engine into usable heat for the cabin.

Multiple components relate to your vehicle’s heating system. This includes the heater core and fans mentioned above but also includes hoses, a control valve, and the climate control system inside your car. It’s important to mention that your vehicle’s cooling system must also be working properly for the heater to function. If any of these components are malfunctioning, it can cause the heating system to stop working altogether.

What Are Common Car Heater Problems?

car temperature control panel

The two main issues you might face are a heater blower not working and a car heater blowing cold air. In essence, these issues are basically the same thing because they translate to no heat. However, the root cause may differ.

If either of these symptoms are happening, you should avoid driving your car in cold weather. Doing so can place you in danger because your vision is impaired. Unfortunately, there are multiple reasons why it might not be working. There’s also the possibility of a more serious issue. 

Why Would a Car Heater Stop Working?

System not blowing air

If there is no air blowing at all it’s usually related to two things:

  • Faulty Blower Fan: If the blower doesn’t work at all, the heat collected in the heater core is not being pushed into the air vents. This can be a result of a faulty blower motor, a blown fuse or an open or short-to-ground blower motor circuit.
  • Faulty Climate Control Switch: Obviously, if the heater switch doesn’t close the blower motor circuit, the blower won’t receive the power it needs to do its job.
  • Faulty Body Control Module (BCM): On more recent car models, especially ones equipped with a smart climate control system, the body control modules is ultimately what’s controlling everything. Smart climate control systems use a thermometer to stop and start the blower when needed so you can just set the temperature and forget it. If for whatever reason, one of the sensors goes bad or if the BCM stops sending a signal back to the controls, the blower will simply not spin at all.

System blowing cold air

Alternatively, if your blower starts blowing cold air instead of hot air, the problem lies elsewhere. Since we know that the blower is working, it can’t be one of the issues listed above. It’s more likely that a plugged heater core or air in your cooling system is causing the problem. The first things to inspect are as follow:

  • Thermostat: A thermostat allows or blocks the coolant from flowing through your cooling system. If it isn’t working and stay open all the time, it will take a lot longer for your cooling system to reach its optimal working temperature and may never reach it at all depending on the car model. When it happens, even though the blower is turned all the way up, the air coming out of the vent will stay cold. 
  • Low Coolant Level: If the coolant level is too low, it’s likely that the coolant won’t be able to reach the heater core. If it’s the case, the heater core will stay cold and won’t be able to transfer any heat to the air flowing through it.
  • Clogged Cooling System: If the cooling system is obstructed somewhere, the hot coolant will, once again, not be able to reach the heater core. That will result in the exact same symptoms as a low coolant level.

How to Fix a Car Heater

Man adjusting car air vent

Fixing your car heater comes down to diagnosing what component is malfunctioning. It’s helpful to first determine if there’s any airflow or none at all. Should there be cold air coming through your vents, then you should be looking at your cooling system and heater core first.

If you suspect your cooling system is to blame, then bleeding the system may help to push out any trapped air bubbles. Inspect the thermostat and make sure it’s in good working order. Check coolant levels and ensure that there are no leaks. In the event that this doesn’t solve it, use a thermometer to check if your heater core is heating up. If it isn’t, flush the heater core and see if that helps. 

If there’s no airflow, you should first look at the blower motor circuit and inspect it for a blown fuse, burnt relay and open or short-to-ground conditions.

Closing Thoughts

Diagnosing a dysfunctional car heating system can be tricky, especially if it’s related to the cooling system. However, a faulty blower motor is usually quite easy to fix. When in doubt, it’s always a good idea to take your car to a trustworthy auto mechanic who can quickly diagnose your non-working heater. To potentially prevent an issue with it, make a point of keeping your coolant levels topped off at all times and don’t neglect routine maintenance.

The main cause for clogs and obstructions causing problems with the coolant’s circulation is usually related to a lack of cooling system maintenance. Never forget that the coolant in your vehicle also needs to be replaced at specified intervals. If you are not sure what the recommended replacement interval is for your vehicle, look for that information in your car’s repair manual.

Unfortunately, there’s not much that can be done to prevent blower motor problems. Like all other electric parts, internal components will wear out with time and will stop working at some point. When it happens, the part will need to be replaced.

In all cases, make sure to diligently fix any heater problems so that your car is always safe to drive!

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About Ren R

Ren R
Loves cars and helping others learn how to take care of their own vehicle. Drives a Honda Accord and enjoys every second of it!

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