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Is Your Car Heater Blowing Cold Air? Here’s What Might Be Happening

The command center for working a vehicle's heating, cooling, and defrosting system.

You may only use your car’s heater for a few months each year, but once you need it, it’s certainly appreciated. Besides making the interior toasty warm, the heater melts snow, clears ice, and otherwise ensures optimum visibility while driving. But what about a car heater blowing cold air or no air at all? With a little context, you or your mechanic can diagnose this problem.

Air Blockageautomotive heater vent

Before checking under the hood, you should rule out an obvious but easy-to-miss answer: closed or blocked vents. Even with the heater operating on a high setting, you may hear only a loud hum. Open every vent in the vehicle, and if dials control the air flow, ensure they’re set to open too. If they’re all open, then lift the hood to look for and remove possible obstructions. Stray leaves can partially or completely block the air intake.

Temperature Controls

Beyond the air circulation, the problem may be with the temperature controls. Turning on the heat and moving it to the warmest setting while the vehicle is running may be exactly how you discovered the issue. But before trying anything else, turn the system off, stop the engine, restart the vehicle and switch on the heat again. Sometimes, all that’s needed is a quick reset. Also, check the fuse box to find out if the fuse supporting the heating, ventilating and air conditioning system has blown. If it has, replace it and try again.

Low or No Coolant

Having too little coolant in your vehicle could cause it to overheat. A low coolant level means there isn’t enough fluid to travel to the heater core to warm your vehicle. Left unchecked, it could damage the engine. Examine the coolant system, check for leaks and broken hoses, then add coolant if needed.

Stuck Thermostat

If the thermostat is stuck open, the engine temperature will drop below normal, especially in cold weather. In this case, the check engine light should be on and a P0128 code activated. When the car is cool, lift the hood and check the hoses for blockages. Otherwise, the valves in the thermostat hoses may be stuck open. Fix or replace stuck valves, or replace the entire thermostat if required.

Faulty Heater Core

Fog or a sweet smell inside your car may point to a worn-out heater core. If the engine is hot but the air coming into the cabin is cool, then it’s likely the heater core has expired. It’s typically located underneath the dashboard, and if it’s leaking, coolant may escape into the cabin. Check the heater hoses first before assuming the core isn’t working. If the hoses are fine, then you’re probably looking at repairing or replacing the core.

Blend Door Actuator

The pocket-sized electric motor known as the blend door actuator controls a vehicle’s climate control system: heating, cooling and defrosting. New vehicles may have two actuators. Both will be located behind the vents. Other than the lack of heat, there are a few telltale signs of a broken actuator: knocking, clicking, inconsistent airflow or the wrong temperature registering on the readout.

Whatever the issue may be, identifying and fixing car heater problems immediately is important, especially when cold weather dominates.

Check out all the heating and cooling products available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on your car heater blowing cold air chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Pixabay.

Matthew C. Keegan View All

Matt Keegan has maintained his love for cars ever since his father taught him kicking tires can be one way to uncover a problem with a vehicle’s suspension system. He since moved on to learn a few things about coefficient of drag, G-forces, toe-heel shifting, and how to work the crazy infotainment system in some random weekly driver. Matt is a member of the Washington Automotive Press Association and is a contributor to various print and online media sources.

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