Is your car heater blowing out cold air?

Before you can determine the problem, you must first know how your car heater works. Remember that the part that transfers heat into the passenger compartment is the heater core. This can be thought of as a mini radiator. The coolant flows through the heater core while the fan, also known as the blower, blows air through the heater core’s fins. When the air blows through these fins, it is heated and that heated air warms the passenger apartment.

Now we can check why your car heater is blowing cold air. You can start by checking the coolant. This coolant is the substance that warms the heater core. Therefore, if the coolant is low, it is possible that that may not be enough to warm the air that blows to the passenger compartment. If you’re wondering, why can’t your temperature gauge just warn you about the low coolant, it is simply because the temperature outside is cold so low coolant may not affect the operating temperature of your engine. Once the coolant is full, put the engine at normal operating temperature. Feel the heater hoses that go through the firewall; they both should be hot to the touch.

If only one is hot, this means that there is a blockage in the heater core or there is air trapped in the heater core. Use a coolant funnel to purge the air from the cooling system. If the coolant is really brown, it has been neglected. If “stop leak” has been used at some point, the heater core could be blocked up. This blockage can be removed by flushing the heater core through the heater hoses using a garden hose with a sprayer.

If neither of them is hot to the touch, there could be a malfunctioning heat control valve. Check for the heat control valve by following the heater hoses back to the engine. There might be a broken vacuum line so the valve cannot operate. And maybe you by-passed the heater core because of a leak, so you looped the heater hoses.

If you are sure that the coolant is in good shape, but cool air is still blowing out your car heater, you can check for proper airflow. Adjust the heat control to the highest and lowest; listen for the movement of the doors within the heater case. These doors can be controlled by vacuum motors, cables or electric actuators. If it is controlled by electric motors, tapping it can sometimes make it work. If it is controlled by cables, find the door that controls the airflow across the heater core. If it is controlled by vacuum motors, the diaphragm needs replacing.

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