Why Is My Car Heater Blowing Cold Air?

There’s nothing much more unnerving and horrible than a car heater blowing cold air in a cozy environment. You should always have a comfortable driving experience whether you’re driving in cozy weather or on a hot sunny afternoon.     

When driving in cozy weather, you will want to switch on the car heater to warm up the cabin. And when cruising on a hot afternoon, you will likely turn on the air conditioner to stay chilled.

If these components fail to work, you’ll not enjoy optimum driving comfort. Here, we’ll discuss why the car heater is not working and blowing cold air. We’ll also explain car heater blowing cold air costs to fix and how to proffer solutions to the underlying problem.

car heater not blowing hot air

What Causes a Car Heater to Blow cold air?

The issues with a car heating system are common and easy to diagnose and fix. The common reasons for car heaters blowing cold air include low engine coolant, broken heater flaps, bad thermostats, and air in the cooling systems. Defective heater controls and clogged heater cores can also be the culprit.

Let’s look at the probable causes in detail.

Low engine coolant level

Engine coolant does not only help with the cooling system maintain normal engine operating temperature. It is also essential for proper heat support in the heating system. The heater air vents will blow cold air if the coolant level is below the recommended level.

Lousy thermostat

The car thermostat ensures your engine gets to the normal operating temperature as soon as possible and keeps it at that level. Therefore, if the thermostat fails, it may prevent the engine from getting up to the average operating temperature. If this happens, the heater will blow lukewarm or cold air, which is different from the air it used to blow.

If the temperature gauge on the dashboard is never getting to the average temp (200 Fahrenheit or 90 degrees), there’s the likelihood you have a malfunctioning thermostat.

Air in the cooling system

Air in the cooling system is a bad omen that you don’t want to happen because it can cause engine overheating and lead to catastrophic engine damage.

Air will likely enter into the cooling system after replacing a related component or if you once had an extremely low coolant level. In rare cases, the air can creep in from a leaky or bad head gasket. As a result, airlocks can get stuck in the heater core, causing the car heater blowing cold air while idling or driving.

Broken heater control

The heating system is operated or controlled with the control buttons inside the car. So, it’s possible everything is working perfectly, but the heater control is broken or stuck. If this is the case, you may think the car heater blower is not working.

Car manufacturers often produce these controls with cheap plastic materials, making them susceptible to damage.

Broken heater flaps/Seized blend door

Regardless of your vehicle design, there should be flaps under your dashboard that control airflow or coolant flow to the heater core. If these flaps bend or the electric actuators get damaged, the heater core will not work as designed. As a result, it can cause the car heater blowing cold air while driving.

If your car uses an electric motor in place of these flaps, your car computer will throw an error code when it detects any issue on the motor.

Clogged heater core

If nothing is working, there’s a huge chance you have a clogged or bad heater core. The heater core is the central or heart of the heating system. So, if it fails, it’ll affect the overall heating system. For example, if the car heater is blowing cold air on the passenger side, you have a failing heater core that needs attention.

How do you test a heater core?

Here are the common steps on how to test a heater core.

  • Switch on the heater and check if heat is entering the cabin. If there’s heat in the cabin, then the heater core is working properly.
  • Examine the coolant level and ensure it is at the recommended level. After that, test the thermostat and ensure it is working properly. There’s a chance that the heater core is bad if the coolant level is okay and the thermostat is working fine.
  • Turn on the engine and allow it to run for a minute or two. After that, switch on the heater and smell the airflow from the defrost vents. The heater core is bad if you perceive a sweet smell like antifreeze.
  • Inspect the carpet on the passenger side. A small sweet smell puddle on the flow shows you a defective heater core.
  • Switch on the heater and visually inspect the air vents. You’ll see puffs of smoke if the heater core is gone.
  • Touch and feel the two hoses that connect to the heater core. If one is cool and the other is warm, there’s a chance the heater core is out.

How To Fix Car Heater Blowing Cold Air

We have seen several probable causes of a car heater blowing warm air only or only cold air, as the case may be. Therefore, there are several ways to fix it.

car not blowing hot air

Refilling coolant

The coolant level is the first and easiest thing you need to check when the heater blows cold air. Park the vehicle on a leveled pavement and allow the car to cool before opening the radiator cap. Once the engine is cool (15 to 30 minutes), open the radiator cover and see the coolant level.

Ensure the radiator is filled to the brim. After that, check the reservoir tank and ensure the coolant is within the recommended level. The reservoir tank has MIN and MAX levels. Fill the tank until it gets to the MAX line. Underfilling or overfilling will cause issues. So, stick with the recommended level.

Replace lousy thermostat

If the thermostat fails, it can either affect the heating system or cause the car engine to overheat. Trust me; you don’t want any of these to happen. If you suspect the thermostat is the culprit, test and replace the thermostat to fix the problem.

Unclog heater core

If you suspect the heater core is the culprit, inspect it. You can fix the problem by flushing the heater core pipes, manually cleaning a blocked heater core exterior, and getting rid of any dirt that caused it. In some cases, you may have to replace the heater core with a new one.

Replace a broken heater flaps/seized blend door.

If a faulty blend door actuator is a culprit, you will have to replace it. You can check out this article, Blend door actuator symptoms: how to test and replace it.

Replace broken heater controls.

If you have a broken heater control, contact a certified mechanic to replace it. As an easy alternative, there are many YouTube videos that will guide you on how to replace broken heater controls. You can watch any of them to have a visual presentation on how to fix it. We recommend you watch this video if you own a Fiesta MK6.

Bleed the cooling system.

If you have trapped air or airlocks in the cooling system, bleed the entire system to remove the air. The process can be difficult, especially if you’re an amateur DIYer. So, it’s better to have an experienced mechanic get rid of the trapped air.

Car Heater Blowing Cold Air Cost To Fix

It’s difficult to accurately say the repair cost of a car heater blowing cold air because several factors can be the culprit. However, the repair cost can be as little as $10 or as high as $1000 or even more.

A low coolant level is one of the common root causes and the easiest and cheapest to fix. If the low coolant level is the culprit, you’ll spend around $10 to fix it. Issues like replacing the heater core and jammed blend door actuators can cause around $400 to $1,000, depending on your car’s make and model.


Why is my car heater not putting out hot air?

As reiterated above, several factors can cause the car heater not to blow hot air as it should. The common reasons why the car heater is not blowing hot air are low coolant level, lousy thermostat, jammed blend door actuator, clogged or defective heater core, broken heater controls, and air in the cooling system.

What do you do when your heater blows out cold air?

If your heater is blowing cold air, have it diagnosed and fixed as soon as possible to enjoy optimum driving comfort on that early morning drive. You could have a low coolant level, broken heater control buttons, or a lousy thermostat. Of course, other issues (as explained above) can be the culprit.

How expensive is it to replace a heater core?

The average cost of replacing a heater core is around $700 to $1,000. This includes parts and labor costs. The replacement cost is way higher than the part itself. Try and get estimates from some repair shops and compare them to know which to go with. If you know your onions and want to replace the component yourself, you’ll only spend $100 to $300 on parts.

How can you tell if your heater core is going out?

Like other heating and cooling system units, a failing heater core will display some symptoms to alert the driver to take necessary precautions as soon as possible. The most common signs that show your heater core is going out are a foggy car interior, a sweet smell inside the cabin, too much coolant loss, a cold passenger compartment, and a hot engine but a cold cabin.

Can low coolant cause no heat?

Yes, a low coolant level can cause no heat. Coolant is responsible for keeping the engine at the normal operating temperature. And it is also necessary for optimum heat support for the heating system.

How can I heat my car without a heater?

There are other creative and cost-effective ways to have heat in your car without a heater. While some of these methods may not be as effective as having a functioning heater, they can keep you warm to an extent.

These include keeping blankets in the back seats, taking warm beverages along, stocking up on hand-warming packets, covering the windshield when parked, and installing a heater seat. The last method is quite effective but can cost more than fixing the car heater.

Is there a fuse for your car heater? 

Yes, your car heater has a fuse. If this fuse is blown, it’ll prevent the heater from receiving electric flow to function properly. You can diagnose the fuses in your fuse box if you think it is the culprit. Follow the instructions on the fuse cover to track the exact fuse for your heater.

Final Words

Several factors can cause a car heater to blow cold air, making it a bit challenging to track the root cause of the problem. Luckily, this article has outlined the possible causes and how to track and fix the culprit. We also explained other means of getting heat in a car without a heater.

Follow the guidelines in this article to fix the problem. However, if you’re an amateur DIYer or do not understand the underhood working principles of a car, contact a certified mechanic to fix the problem.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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