If you want to know the answer to the question why does my car heater blow cold air, there could be a problem with a part in the cooling or HVAC system. Follow the steps in this article and video and find out how to diagnose heat blowing on one side but not on the other yourself.
Why Does My Car Heater Blow Cold Air When I Turn the Heat On?
If you have a car heater that blow cold air when you turn the heat on, you may have a problem with a part in the cooling system like the heater core, blend door actuator, or HVAC controls.
How to Inspect a Car with a Heater That Blows Cold Air
We use a 2008 Chevy Silverado truck in this example, but these steps generally apply to other makes and models
Steps to take if you want to know why the heater in your car is blowing cold air
- Check the Coolant Level with the Engine Cold
While the engine is still cold, check the coolant level. Remove the cap from the coolant reservoir. If needed, shake the reservoir and make sure there’s enough above the minimum level.
If the car has low coolant, it could lose flow to the heater core before the engine. Since coolant is needed for the engine to work, you’ll want the coolant level to where it should be.
Once you’ve checked the level, top it off with the appropriate coolant.
- Check the Heater Pipes
Check the heater pipes that enter the firewall. There should be two off the water pump that coolant travels through. With the engine warm, if you measure their temperature or carefully feel them with gloves for safety and they’re ice cold, that means coolant isn’t flowing. You could have a plugged heater core or water pump that isn’t pumping.
If the water pump wasn’t pumping, you’ll probably have an overheating issue and the temperature gauge will be in the red.
- Check the Coolant Temperature When Driving
When driving, the next thing you’ll want to do is check the coolant temperature. With the key and accessories on, you can see the temperature gauge in its default, down position. Start the engine and run it for a while. After about 10 to 15 minutes, the gauge should go up to around 210 degrees. If it’s not near 210 degrees or close, there could be another problem. There could be a thermostat stuck open or a cooling fan stuck on. Make sure the engine is actually warming up so you know the hot coolant is getting to the heater core.
- Make Sure the HVAC Actuator Doors Are Opening and Closing
If you notice the heat blowing on one side in your car, make sure the blend door actuators in the HVAC system are opening and closing. This means you’ll be able to transition from hot to cold.
Turn the key on and start the engine. Turn the blower motor/fan settings to MAX and the airflow to LOW, and have air flowing from the vents. With air flowing, put the heat on. In our example, there’s less airflow with the heat on. We know the blend door actuator is moving / opening and closing.
More on how blend door actuators can affect the interior temperature
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Follow the step-by-step instructions from our expert mechanics in our how-to videos and learn how to replace different parts in many different models yourself.
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