Heater Performance Test

Review Safety Warnings and Cautions before performing this procedure.

Check the coolant level, drive belt tension, vacuum line connections, radiator air flow and fan operation. Start engine and allow to warm up to normal temperature.

WARNING: DO NOT REMOVE RADIATOR CAP WHEN ENGINE IS HOT, PERSONAL INJURY CAN RESULT.

If vehicle has been run recently, wait 15 minutes before removing cap. Place a rag over the cap and turn it to the first safety stop. Allow pressure to escape through the overflow tube. When the system stabilizes, remove the cap completely.

MAXIMUM HEWER OUTPUT TEST AND ACTION
Engine coolant is provided to the heater system by two heater hoses. With the engine idling at normal operating temperature, set the temperature control to maximum heat, the mode control to the floor position, and the blower in the highest speed position. Using a test thermometer, check the temperature of the air being discharged from the floor outlets. Compare the test thermometer reading to the Temperature Reference chart.

Temperature Reference Chart:

Both of the heater hoses should be HOT to the touch (coolant return hose should be slightly cooler than the supply hose). If the coolant return hose is much cooler than the supply hose, locate and repair the engine coolant flow obstruction in the heater system. If both heater hoses are cool to the touch, inspect the engine cooling system.

OBSTRUCTED COOLANT FLOW Possible locations or causes of obstructed coolant flow are as follows:
- Pinched or kinked heater hoses.
- Improper heater hose routing.
- Plugged heater hoses or supply and return ports at the cooling system connections.
- Plugged heater core.

If proper coolant flow through the cooling system is verified, and heater outlet air temperature is insufficient, a mechanical problem may exist.

MECHANICAL PROBLEMS Possible causes of insufficient heat due to mechanical problems are as follows:
- Obstructed cowl air intake.
- Obstructed heater system outlets.
- Blend door not functioning properly.

TEMPERATURE CONTROL
If the heater outlet air temperature cannot be adjusted with the temperature control knob on the A/C-heater control, the following could require service:
- Blend door binding.
- Faulty blend door motor.
- Faulty A/C-heater control.
- Faulty related wiring harness or connectors.
- Improper engine coolant temperature.