Car Heater Troubleshooting

car heater not hotMy car heater blows cold air. I replaced the thermostat and had the heater core flushed three times ( once was professionally done).

I’m not sure what else could be the problem so any information will be helpful. The temperature gauge reads normal temp and the truck is not over heating. This has become very frustrating for me since the weather is still somewhat cold. Thanks for your time and help. Hope to hear from you soon




Howdy Rollie,

I would first feel the two small rubber heater hoses located under the hood on the passenger side from the engine to your heater core which is also located on the passenger side with your bare hands. Start the engine and let it warm up to operating temperature, and feel those two heater hoses they should be VERY hot to the touch.


How To Diagnose A Heater Problem

1. If you feel those two heater hoses and they ARE hot, then you probably have a control problem inside the dash not switching from A/C to heat or a problem with the push button control head itself in the dash.

If the hoses are hot, there is HOT coolant circulating throughout the system and the heater core itself. Something is not moving the air diverter door inside the dashboard to the heat selection.

The heater core heats up with the hot coolant and air is diverted over the heater core allowing hot air to be blown into the cab of the vehicle. The opposite happens with the A/C, Freon gas is sent inside dashboard to the Evaporator core, which gets very cold and air is then diverted across the evaporator blowing cold air inside the cab. Like an ice cube in your hand as you blow over it.

2. If the two heater hoses are cold you probably have a low coolant flow issue. The water pump could have a problem, the radiator could be stopped up with rust, a heater hose could be stopped up with rust or kinked…something is NOT circulating hot coolant throughout the engine.

A bad thermostat can also be the culprit and since its easy and cheap to replace I usually install a new thermostat as my first guess to rule things out.

3. If one heater hose is hot and the other is cold, you have a restriction in the heater core and it should be replaced, but I don’t think that is the issue. If this is happening though, you can try adding a flush kit to the heater hose and attach a garden hose to it to try and flush out any rust or debris that might be restricting coolant flow inside the heater core. But since you already did that….

Flushing a dirty heater core

Here is how you can do that.

Posted in: A/C and Heater

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."
  • Louis

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