Car Heater Blowing Cold Air: 5 Common Causes

Finding out the heating system in your vehicle is fundamental for any car owner. When winter hits, the heating system in a car releasing cold air is the last thing you’d want to deal with. This article will help you understand the possible reasons behind this issue and how to diagnose it.

How Car Heating System Works

Normally, the car’s heating system is closely tied to the engine’s cooling system. It uses the heat from the engine coolant to warm up the air inside the car. Therefore, when you turn on the heater, the hot coolant is directed through a heating coil. Moreover, a fan blows over this coil, and the warm air is distributed throughout the car.

Common Causes of Car Heater Blowing Cold Air

Low Coolant Level

The most common problem is the coolant in your car. This function is essential for the heat exchange process that warms the air blown out by the heater.

Therefore, if the coolant level is low, there’s simply not enough heated fluid to sufficiently warm the air. This can be due to a leak in your coolant system, or it could be that the coolant hasn’t been topped up in a long time.

So, regularly checking and maintaining the coolant level is crucial to ensure the functions properly.

A low coolant level could cause the heater blows cold air

A Faulty Thermostat

Next is the thermostat, which is responsible for regulating the flow of coolant based on the engine’s temperature.

Normally, the thermostat remains closed when the engine is cold, allowing the coolant to heat up. Once the engine reaches its operating temperature, the thermostat opens to allow coolant to circulate and maintain the engine temperature.

Therefore, if the thermostat is stuck in the open position, the coolant is always circulating, not giving it enough time to heat up before it reaches the heater core. This leads to this component blowing out cold air. Hence, replacing a faulty thermostat is usually the best course of action in this case.

Blocked Heater Core

Moreover, the cause is the heater core, which is a small radiator-like device that the coolant flows through. The air typically from the blower motor is heated as it passes over the hot heater core before it’s sent into the cabin.

However, over time, this component can become blocked with rust or debris, preventing the hot coolant from passing through it. As a result, the air blown out by the heater isn’t warmed up, causing the heater to blow cold air. So, a coolant system flush or this component replacement might be necessary in this case.

Damaged Heater Controls

Additionally, heater controls are also a reason. Normally, they will help regulate the mix of hot and cold air in your car.

If these controls are damaged, they might not be able to properly adjust the proportion of hot and cold air, causing the heater to blow out cold air. This could be due to a broken control valve or a malfunctioning blend door actuator.

Therefore, if the blend door is stuck in the position where it only allows cold air to pass. You’ll experience cold air from the heater. In such cases, repairing or replacing the damaged components would be necessary.

Damaged heater controls cause the heater blows cold air

A Broken Blower Motor

Finally, the reason is the blower motor in your car. This component is responsible for blowing air across the heater core and into the cabin.

If the blower motor is broken, it won’t be able to blow air across the heater core, meaning no air (hot or cold) will enter the cabin. Hence, this can make it seem like your car heater is blowing cold air.

So, if you’re not hearing the usual sound of the blower when you turn on this heater, this might be the issue. A blower motor replacement would likely be the solution in this case.

How to Diagnose Car Heater Problems

To determine the problem with this car’s components, you need to investigate the following issues. Here are some detailed tips:

Inspecting the Coolant Level

You can start diagnosing the problem by inspecting the coolant level in the radiator.

In detail, to check the coolant level, first, make sure the engine is cool. Then, continue opening the hood of your car and locate the coolant reservoir. In the process, there should be markings on the side indicating the minimum and maximum levels.

If the coolant is below the minimum level, you need to add more. However, low coolant can indicate a leak in the system, which would need to be identified and fixed.

Checking the Thermostat

If the coolant level is fine, the next step is to check the thermostat. You can do this by feeling the temperature of the upper radiator hose when the engine is fully warmed up. Note that if the hose isn’t hot, the thermostat is probably stuck open and needs to be replaced.

Examining the Heater Core

If the heater core is clogged or blocked, the hot coolant can’t flow into it, and thus the air that is blown into your car isn’t heated.

Therefore, you can check this by feeling the two hoses that go into the heater core. If they have a problem, they may need to be flushed or replaced.

Assessing Heater Controls

Normally, the heater controls in your car allow you to adjust the temperature of the air that is blown into the car’s interior. Therefore, if these controls are not working properly, they may not be able to adjust the blend of hot and cold air. As a result, the heater blows cold air.

So, you can test the controls by adjusting the temperature and seeing if the air temperature changes. If there’s no change, the controls might be faulty and need to be replaced.

Verifying the Blower Motor

Lastly, to verify the blower motor, you can listen for any unusual noises when you turn on the heater. If it’s unusually quiet or makes strange noises, the blower motor might be broken.

Should check the blower motor

Preventing Future Issues with Your Car Heater

Regular maintenance is key to preventing future issues with your car heater. So, make sure to check your coolant level and replace it when necessary regularly. Additionally, inspect the thermostat and heater controls for any signs of damage. It’s important to get a professional to inspect the heater core and blower motor during your regular car service.


The heating system in a car releasing cold air can be a sign of several issues, from low coolant level to a broken blower motor. Understanding the common causes and how to diagnose them can ensure a warm and comfortable drive even in the coldest winter. Remember, regular maintenance is key to preventing these issues.


  1. Why is the heating system in a car releasing cold air?

    There could be several reasons for this, including a low coolant level, a faulty thermostat, a blocked heater core, damaged heater controls, or a broken blower motor.

  2. How can I diagnose a faulty thermostat?

    You can diagnose a faulty thermostat by feeling the temperature of the upper radiator hose when the engine is fully warmed up. If the hose isn't hot, the thermostat is probably stuck open.

  3. How often should I check my car's coolant level?

    It's recommended to check your car's coolant level every time you fill-up the gas tank, especially during the winter months. This could help you keep your car running smoothly and avoid unpleasant surprises.