Car Heater Not Working?

Mechanic Tips to Diagnose a Car Heater Blowing Cold Air

Heater not working on car or truck | dash controls

Not sure why your car heater is not working? Our mechanic shows you how to check your coolant level, heater hoses, coolant temperature, and blend door actuator. These are some of the most common things that cause heater problems.

Diagnose No Heat in Your Car or Truck

1. Check the Coolant Level

Checking coolant levels in reservoir | Heater blowing cold air

The first thing you want to do is check the level of your coolant. Only do this when the car is cold and not running. You can shake the coolant reservoir to get a better reading on the coolant level. If it’s low, you’ll need to top up. 

When the engine warms up, hot coolant is transferred first to the heater core. The heater core is a device that resembles a radiator and is located under the car’s dashboard. It’s designed to conduct the heat from the coolant. This heat is then blown into the cabin as hot air by a fan. 

If your coolant is low, it may not be enough to reach the heater core. This means that you’ll have no heat in your car whenever you need it. Your coolant level should always be between the low and high markings found on the side of the reservoir. 

2. Check the Heater Hose

Checking Heater Hoses or pipes for leaks.

The heater hose circulates the car’s coolant from the engine to the heater core. Since the heater core is located under the dashboard, they run through the car’s firewall. They typically extend from the water pump or engine. 

If you check your heater hoses and realize they are ice cold, chances are they are not circulating the coolant. This means that there’s no heat in that’s reaching the core and hence, no heat in your car. 

It could be due to a plugged heater core or a water pump that’s not working. In case of the latter, you may also experience an overheating engine or a temperature gauge that’s in the ‘red zone.’ 

3. Check Coolant Temperature

checking the coolant temperature on dash

The next thing you want to check is the coolant temperature. Start the car while the temperature gauge is at its lowest. This should be at around 160° Fahrenheit. Let the engine run for about 10-15 minutes. The gauge should go up to about 210° Fahrenheit. 

If it doesn’t hit that 210° mark or even get close, you could have another problem such as a thermostat that’s stuck open or a coolant fan that’s sticking. You want to make sure the engine is warming up enough to transfer heat to the heater core. If that doesn’t happen, you’ll have no heat in your car. 

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4. Test the Blend Door Actuator

Mechanic showing turning on the ignition to test why there's no heat in your car

A blend door is a small plastic panel that opens and closes to control the flow of air into the cabin. It’s controlled by an actuator or motor that receives signals from the car’s climate control system. 

When you change the temperature from hot or cold or adjust the intensity of airflow, the signals get to the blend door actuator which then adjusts the blend door using plastic gears. To test your blend doors, switch on the car and turn the blower motor on. You can put it on MAX. 

Adjust the vents to allow airflow into the car then simultaneously switch from cold to hot.  As you change the temperature, the blend doors should open or close fully or partially to allow cold or hot air inside. Pay attention to the intensity of airflow as well. 

If the blend doors don’t work, you’ll be stuck with one temperature setting. In this case, it could be just cold air and no heat in the car. Have the blend door actuator checked if your car does not produce any heat. 

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