how to fix an automotive heater?DNT Tools

Tools and Supplies Needed

• Flashlight
• Screwdriver set
• Protective gloves and eyewear

Begin with the vehicle on level ground, engine off (cold) in park with the emergency brake set.

Step 1 - A heater cannot operate unless the engine is full of coolant/antifreeze.

Step 2 - The heater control air blend door is controlled by a electronic/vacuum/cable which can malfunction causing a problem. Check the door operation by moving the heat control from hot the cold while listening for moment inside the heater plenum. (Note: This works better with the engine off.)

Step 3 - Inspect heater system vacuum lines especially to the heater control valve. These vacuum leaks can cause the system to not function. If a hissing noise is present under the dash when the engine is running a vacuum leak exists and must be repaired to restore the heater functionality.

Step 4 - The heater control valve prevents the flow of coolant into the heater core during the air-conditioner function, occasionally this valve will stick not allowing hot coolant to flow, inspect the valve for movement while in operation.

Step 5 - Use a vacuum gauge to test various control tubes which are used to move blend door actuators, also use a hand held vacuum pump to test servo diaphragms by connecting to the vacuum port directly. If no vacuum is present, open the hood and inspect all small vacuum lines from the engine to the firewall and under the dash, this test can be used for the heater control valve as well.

Step 6 - The heater core is responsible for converting hot coolant into heated air, if this core becomes plugged it will not operate correctly. To check for a plugged heater core, start the vehicle and allow the engine to warm up to normal operating temperature while turning the heater to its hottest setting. Grasp both heater hoses, they both should be hot, if only one is hot, the core could be plugged or the heater control valve is malfunctioning.

Step 8 - An air cabin filter helps clean the air before it enters the passenger compartment, when this filter becomes plugged it stops the airflow and needs to be replaced.

Helpful Information
Sometimes engine coolant level can be low without the engine overheating, especially in winter conditions. A heater control valve can be actuated by either a vacuum line or control cable. To warm the passenger cabin, the heater system makes use of heat generated from the engine by blowing across the heater core and onward through the system ductwork. When a heater core develops a leak, there are usually two indications, steam could be produced from the vent system and is accompanied by a pungent odor, or the passenger floor can become wet from leaking coolant, these are signs the core needs replacement.