Heater Performance Test

PRE-DIAGNOSTIC PREPARATIONS
Review the Safety Precautions and Warnings before performing the following procedures.

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

WARNING: DO NOT REMOVE THE RADIATOR CAP WHEN THE ENGINE IS HOT. PERSONAL INJURY MAY RESULT.

If the engine has been operating, wait 15 minutes after the engine is turned OFF before removing the cap from the radiator. Place a rag over the cap and turn it to the first safety stop. Allow pressure to escape through the overflow tube. When the cooling system stabilizes, remove the cap completely.

MAXIMUM HEATER OUTPUT: TEST AND ACTION
Engine coolant is provided to the heater core through two 16 mm (5/8 inch inside diameter) heater hoses With the engine idling at normal operating temperature, set the heater-A/C controls as follows:

Temperature Reference Chart:

Temperature control to full Heat, Mode control to Floor, and Blower control to the highest speed setting. Using a test thermometer, check the air temperature coming from the floor outlets. Refer to the Temperature Reference Chart.

If the floor outlet air temperature is insufficient, refer to, Cooling System for specifications. Both heater hoses should be HOT to the touch (the 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.

POSSIBLE LOCATIONS OR CAUSE OF OBSTRUCTED COOLANT FLOW
- Pinched or kinked heater hoses.
- Improper heater hose routing.
- Plugged heater hoses or supply and return ports at the engine cooling system connections, refer to, Cooling System.
- Plugged heater core.
- Air locked heater core.

If coolant flow is verified and heater floor outlet temperature is insufficient, a mechanical problem may exist.

POSSIBLE LOCATION OR CAUSE OF INSUFFICIENT HEAT
- Obstructed cowl air intake.
- Obstructed heater system outlets.
- Blend-air door not functioning properly.

TEMPERATURE CONTROL
If heater floor outlet temperature cannot be adjusted with the heater-A/C control Temperature knob, one of the following could require service:
- Blend-air door binding.
- Faulty temperature control cable.
- Improper engine coolant temperature.
- Faulty heater-A/C control.