As winter rages across most of the country, your car’s heating system becomes important for several reasons. While any mechanical component can fail at any time, proper maintenance could keep the warm air flowing and save a trip to the repair shop. We’ll provide four fundamental reasons the heater in your car might not work and their solutions. 

Why is a car’s heater important?

Your car’s heater does more than keep you warm when the weather turns cold. It also provides heat to clear your windshield, side window, and sometimes your outside mirrors on frosty mornings. 

In extreme winter weather conditions, your heater works to keep your windshield from icing over and could provide enough heat to save your life should you become stranded in your car in a snow bank. 

How does a car heater work?

Unless you have an electric vehicle (EV) or an older air-cooled VW Beetle, your car’s heater gets heat from the engine’s hot antifreeze, also known as engine coolant. 

Are you confused yet? If not, that’s good, but if you are, you’re not alone, so let’s dive deeper. 

The water that keeps your car from overheating contains antifreeze to keep it from, you guessed it, freezing in cold temperatures. We call this mixture engine coolant because that’s its primary purpose.

Automotive engineers route this hot coolant through a small radiator typically located under your dash and use a fan to blow air through it. Like the radiator in the front of your car, this small radiator, called a heater core, heats the air blown through its fins. The warm air blows through ducts to your defroster, in-dash vents, and underneath to your feet. 

Four common reasons your car’s heater isn’t working and what to do

Low engine coolant level is one of the most common reasons your car’s heater isn’t working. Since the engine coolant’s primary mission is keeping the engine cool, it won’t send heated coolant to the heater core if the system operates at low levels. 

Checking your car’s coolant level and keeping it topped off will prevent overheating in the summer and ensure your windows defrost that first cold winter morning. It’s also an excellent method to keep an eye out for coolant leaks. But first, it’s critical to ensure the engine is cool before opening the coolant tank cap. 

According to RepairPal, air-lock is another common issue that keeps the hot coolant from reaching the heater core. Air-lock happens when coolant leaks out of the system or sometimes when adding coolant back into the system when it’s low. 

The solution requires starting with a cold engine after sitting for several hours (overnight is safest), then opening the coolant tank cap and turning the heater on full blast before starting the car. As the car warms up, the coolant will cycle through the system and “burp” any air-lock bubbles, dropping the coolant level. 

Next, refill to the “Full” line, reinstall the coolant tank cap with care, and go for a test drive. Be sure to check for leaks under the car when you return.

A clogged heater core prevents hot coolant circulation and limits heat transfer to the fan-blown air. Once it’s plugged up, it’s only a matter of time before it fails and begins to leak into your car’s interior. The good news is that heater core clogs are usually preventable.

While flushing your coolant system is an intermediate DIY procedure, it only requires standard tools. Your car’s owner’s manual has a schedule for various maintenance tasks, and coolant flushing is one of them. If you feel uncomfortable doing it yourself, it’s a standard procedure available at any automotive repair shop. 

Another common issue is when no air comes out of the vents, not even cold air. Most of the time, this is due to a blown fuse that should provide power to the heater’s fan. 

Again, turning to your car’s owner’s manual will guide you on which fuse it is and where it’s located. Next, visit your local auto parts store for replacement fuses and the small tool used to remove and replace them. 

A word of caution: if the fuse fails again quickly, take your car to a mechanic, as it could indicate a potentially dangerous electrical problem.