My Car’s Heater Isn’t Working – Help!

heating vent and control panel in a car

Getting Your Car Heater Checkup

Boy, it has been a hot summer, hasn’t it? Can you believe fall and winter are around the corner already! What that means is it’s time to make sure your car heater is working NOW, before those temps hit 32 degrees. Just like the heating system in your home, your car heater needs a preliminary winter checkup too. 

With that in mind, we’re going to answer some common questions about car heaters. Some of the questions are basic and some are for those of us that didn’t get that preliminary winter checkup on our car heater. Because if your car heater isn’t working, the ride is going to be miserable and your teeth are going to be chattering, not to mention, it’s hard to drive if you’re shivering! 

Did you know that when the car heater isn’t working correctly, your car can overheat just like it does when the air conditioner isn’t working correctly?  Interesting, huh? So, how does a car heater work? Let’s take a look.

The Facts on Car Heater Operation

A car heater is connected to functions beyond keeping the interior of your car warm. A car heater has two jobs: heating the interior of your car and keeping the engine cool. The key components of a car heater are: 

  • The Heater Core
  • The Blower Motor
  • Heater Hoses
  • The Heater Control Valve
  • The Control Panel

A car heater also interacts with the car’s cooling system, which includes: 

  • The coolant
  • A thermostat
  • The radiator
  • The water pump 

The engine generates heat, and to keep it from overheating, it has to go somewhere, yet keeping the interior of the car on an Illinois winter morning is important.  Most of that generated heat exits through the exhaust system and the remaining heat is transferred into the coolant inside the car’s HVAC system, much the same way it works on your home’s HVAC system. 

As that engine-generated heat leaves the radiator where the coolant is located, it moves to the heater core. The heater core is a heat exchanger and as the heated coolant flows through it, the heater control valve regulates the heat. It is at that point your car heater warms up to the level the HVAC control panel is set, and then it blows out through the vents. 

Why is my car heater not blowing air?

On that first cold Illinois winter morning when the heat doesn’t get warm after a couple of minutes, what is the problem?  Well, there are a few things that could be the problem that is keeping your car heater from heating up: 


It takes an almost exact mixture of antifreeze and water to create an ideal coolant for your car engine. This keeps the engine from freezing up and cracking or overheating in the summer. It ensures the cooling system is absorbing and dissipating the heat from the engine effectively.

During the winter, with the HVAC controls set on heat, some of that excessive engine heat blows into the cabin of your car and through the windshield defroster. Over time, that coolant can get contaminated and not as effective in keeping the engine cool and the heater blowing warm.


The heater core looks like a smaller radiator with fins and narrow tubes. It dissipates that generated heat into the surrounding air as it heats, and the blow fan blows it into the car cabin.

Like the car radiator, the narrow tubes can become clogged or start leaking. This will reduce the coolant flowing through the cooling system. The longer it stays clogged, the better the chance it will contaminate the coolant, and then you have two problems with your car heater. 

You can often tell when the heater core is clogged or not working by a sweet smell inside your car. Other indicators are that the windows won’t defrost and there is moisture, even puddles, on the front floorboard. 


A car’s thermostat is a valve that regulates the coolant flow by opening and closing. While this may sound simple, if the thermostat isn’t functioning right, it can overheat the engine or keep the car heater from heating up. A damaged or malfunctioning thermostat is one that is stuck in one position or the other.


When you turn the car heater up, the heater core grabs heat from the coolant, and then transfers it inside the cabin, giving you that warm air you want. The blower fan is how that air is moved into the cabin and if it isn’t working, then the warm air isn’t getting inside the cabin. This could be because of a blown fuse, loose electrical wiring, or because the blower motor has simply quit working, and your car heater isn’t heating up the inside of your car. 

What do you do when your car heater is blowing cold air?

There are several things that can keep a car heater from blowing warm air as we just discussed. So now you may be asking, “How do I fix the heat in my car?” The following is a list of the most common causes found and suggestions on how to fix them.

The Engine’s Thermostat

My Car’s Heater Won’t Turn Off! You don’t hear that much during the winter, but it can be an uncomfortable problem. This is a valve that controls how the coolant flows to the radiator. When a car is first started, the thermostat stays closed until the engine reaches a certain temperature. Then it opens up and allows the coolant to flow through the radiator to keep the engine from heating up too much. 

When the thermostat goes bad, it will often get stuck either opened or closed. A thermostat stuck open will allow the coolant to keep flowing through, never having time to heat up. If the thermostat is stuck closed, the coolant won’t flow and the engine can overheat, causing a lot of damage fast. Changing the thermostat will fix this problem either way. 

Low Coolant Level

The coolant fluid supports the heating system and when there isn’t enough coolant, the car heating system can’t get what it needs to blow warm air inside your car.  When a car’s coolant level is low, it is usually because there is a coolant leak at one of the connections, hoses, at the radiator, or any of the many other components. Adding coolant to the radiator will usually fix this, maybe only temporary if there is a leak.

Cooling System Has Air Bubbles

If your car heater is blowing cold air, there may be air bubbles in the coolant, keeping the engine-generated heat from transferring to the coolant.  The air bubbles need to be released for the car heater to start working correctly again. This can be done with the following steps: 

  • Set the heating control system to maximum 
  • Remove the radiator cap
  • Add coolant to the radiator’s maximum level
  • Start the car and allow to idle with the radiator cap off
  • Add more coolant if needed after the thermostat opens
  • The air bubble should start leaving the coolant at this point
  • After the car engine is warmed up, replace the radiator cap, and start try the car heater again

Heater Core Issues

Your car heater may be blowing cold because the heater core is stopped up. Remember, the heater core is like a small radiator and if the narrow tubes get a clog, the coolant can’t flow through and warm the car heater. To unclog the heater core, do a manual flush to remove whatever debris is clogging the narrow tubes. If flushing doesn’t fix it, you’ll need to have a new heater core installed. 

Heater Control Issues

Sometimes the problem with a car heater system isn’t internal, but with the heating controls. Over time, the buttons become clogged and stick, or simply break after a lot of use. The best fix for this is to have the buttons replaced. 

Blender Door Jammed

Part of your car heater is the air blowing through the vents. These are controlled by a blender door and if it becomes jammed or stuck, it can’t open to allow the warm air out. Or it becomes stuck open, and the warm air won’t quit coming inside the cabin. The only fix for this car heater issue is to replace the blender door. 

Will a car heater work without an AC compressor?

The air conditioning compressor in your car isn’t just for cool air in the summer. It has other jobs year-round, like keeping the windows defrosted. It also keeps the heat setting controlled. 

How can you tell if you have a bad heater core?

A heater core problem is unique, and not in a way you want to experience. It can actually leak inside your car instead of outside and under your car. A bad heater core can be a messy experience and you’ll know when it is bad or going bad by any of the following: 

1. There is little to no heat in the car 

2. The smell of coolant is inside your car 

3. The windows stay fogged up

4. The floorboard is wet with coolant 

5. The coolant level is low and keeps dropping

6. The engine is running hot

What happens if you don’t replace the heater core?

A faulty heater core will cause the engine to overheat. An overheated engine can do expensive and extensive damage fast. A clogged heater core can cause an engine to overheat because it isn’t getting the right coolant circulation.

close-up of car heater controls

In Closing 

So, maybe you try all the things we’ve suggested, and your car heater still isn’t working right. This means to have a comfortable warm car this winter, you need to take it to a mechanic. How expensive is it to fix a car heater? Well, it isn’t going to be cheap!  One thing we can tell you is that not every mechanic or repair shop will have the same pricing. They have their own labor and overhead expenses to cover. It will also depend on your car’s make, model, and year, as well as what the problem is with the car heater. A rough estimate would be somewhere between $500 and $1000.00. If you’re looking for a true estimate on this kind of job reach out to us today by calling at 630-932-4427.