Car Heater is Blowing Cold Air? (7 Causes & How To Fix it)

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Video Heat in car not working

Driving during the winter season can be very unpleasant, especially if you do not have a working heater in your car.

There is simply nothing like a nice heater to keep you warm and stuffy in your car.

Unfortunately, problems with the heating system are quite common. In this article, we discuss the most common reasons why you don’t have heat in your cabin.

The most common reason a car heater is blowing cold air is due to a low coolant level, a malfunctioning thermostat, broken heater flaps, or air in the cooling system. It can also be caused by a clogged heater core or faulty heater controls.

Here is a more detailed list of the common causes of why the heat is not working in your car:

Car heater is not blowing cold air Causes

1. Low Coolant Level

Low Coolant Level

The most common problem when the heat is not working in your car is actually a low coolant level.

Luckily, the coolant level is very easy to check. Locate the coolant reservoir (Usually a red, green or blue fluid). In most car models it does also says coolant in text on the cap of it. Check the service manual of your car if you are not sure about which reservoir to look for.

You should also find a MAX and MIN sign on the reservoir. If the level is under the MIN sign or you can’t see any coolant there at all it is definitely time to refill it.

Beware that coolant reaches boiling temperatures and it should never be opened when the engine is hot!

If the coolant level has become too low it may actually have caused air bubbles in the coolant systems and you may need to bleed the car’s cooling system after the refill. All of this we will come into further down in the article.

If you have a low coolant level you may have a coolant leak that you need to get fixed as soon as possible.

Find more information here: How to Fix a Coolant Leak

2. Malfunctioning Thermostat

Thermostat Housing

The thermostat is making sure that your car engine is heating up fast and holds a steady temperature when the engine is warm.

If the thermostat fails, it can cause the engine to not reach the working temperature at all, and therefore you will feel that the car’s heating system is blowing warm air but far away from the temperature it was blowing before.

If you see on your temperature gauge that the car is never reaching the working temperature (200 Fahrenheit or 90 degrees), there is a big risk that something is wrong with your thermostat.

Find more information: Symptoms of a Bad Thermostat

3. Broken Heater Flaps/Blend Door Actuators

Blend Door Actuator

There are flaps under your dashboard that regulate either the airflow or the coolant flow through the heating core. If one of these flaps or the electric actuators to them is defective, there is a great risk that your heater will not function as suggested.

If you have a newer car with electric motors for the flaps – you will most likely get an error code on them when you scan the system with a diagnostic computer.

You can also locate the flaps and see if they move when you change the heater control. If they do not – they are most likely broken. It can be difficult to see them on many car models as they are often hidden very deep down under the dashboard.

It also happens that these actuators lose their programming, and they need to be preset with a diagnostic scanner again.

4. Air in the Cooling System

Bleeding Coolant System

Air inside the coolant system is a very bad thing because it can cause overheating of your engine, which can cause severe damages to your engine.

Air can come into the coolant system if the coolant level was once very low or if you replaced any parts in the coolant system recently. In rare cases, it can also come from a bad or leaky head gasket.

Airlocks often get stuck in the heater core inside the car, making the car’s heater blow cold air.

To get rid of air in the cooling system, you have to bleed the car’s cooling system. The process can be pretty difficult if you do not have the knowledge, so I recommend letting a repair shop do it for you.

If you feel that you are comfortable enough to bleed it, you can follow our guide here: How to Bleed Your Car’s Cooling System

5. Broken Heater Controls

Heater Controls

The heating is operated via a series of controls that are available inside the car. You can change the temperature and other settings while sitting in your car. Therefore, it is possible that only the controls are stuck or broken.

These controls are often made of cheap materials like plastic, which makes them very vulnerable to damage. Many YouTube videos on the internet show you how to repair the heating controls.

Older cars used wires from the heater control to the actuator, and it happened that plastic things the wires were pulling on broke. You do often have to replace the heater control unit for this, unfortunately.

Newer cars do often use totally electronic heater control units. Luckily, it is very rare that these fail, but you have to replace the whole unit if they do.

6. Clogged Heater Core

Heater Core Car

If nothing seems to be working, it is possible that your heating core has gone bad or clogged. The heating core is the heart of the heating system, so your entire heating system will fail if the heating core fails.

It sometimes happens that the heater core is getting clogged from rust and other dirt inside the cooling system. Sometimes it is enough to flush the heater core to get rid of this, but sometimes you have to replace the whole heater core.

Here is a video of how to flush the heater core: How to flush a heater core

The heating core is an expensive component, and replacing it is often a challenging task as it is often installed deep under the dashboard. The mechanic would charge you about $600 to $1000, depending on your car’s make and model.

No Heat in Car FAQ

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