Heater Performance Test

PRE-DIAGNOSTIC PREPARATIONS
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, SEVERE PERSONAL INJURY CAN RESULT.

If vehicle has been run recently, wait until engine is cool before removing cap. Squeeze the radiator hose to check temperature, and for pressure in the system. If the hose is very firm, allow time to cool down. 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.

Temperature Reference Table:

MAXIMUM HEATER OUTPUT: TEST AND ACTION
Engine coolant is provided to the heater system by two 19 mm (3/4 inch inside diameter) heater hoses. With engine idling at normal running temperature, set the control to maximum heat, floor, and high blower setting. Using a test thermometer, check the air temperature coming from the floor outlets. Refer to Temperature Reference Table.

If the floor outlet air temperature is insufficient, refer to Cooling for specifications. Both heater hoses should be HOT to the touch (coolant return hose should be slightly cooler than the supply hose). If coolant return hose is much cooler than the supply hose, locate and repair engine coolant flow obstruction in heater system.

POSSIBLE LOCATIONS OR CAUSE OF OBSTRUCTED COOLANT FLOW
1. Pinched or kinked heater hoses.
2. Improper heater hose routing.
3. Plugged heater hoses or supply and return ports at cooling system connections, refer to Cooling.
4. Plugged heater core.
5. Air locked heater core.
6. If coolant flow is verified and outlet temperature is insufficient, a mechanical problem may exist.

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

TEMPERATURE CONTROL
If temperature cannot be adjusted with the TEMP knob/button on the control panel, the following could require service:
1. Blend door binding.
2. Faulty blend door actuator.
3. Improper engine coolant temperature.
4. Faulty A/C Heater Control.