Heater Performance Test

Before performing the following tests, perform the ATC Function Test using the DRBIII(R) and refer to Cooling for the procedures to check the radiator coolant level, serpentine drive belt tension, radiator air flow and the radiator fan operation.

MAXIMUM HEATER OUTPUT
Engine coolant is provided to the heater core through a heater valve and heater hose. With the engine idling at normal operating temperature, set the heater-A/C controls as follows:
- Temperature control in the full hot position
- Mode control in the floor heat position
- Blower motor control in the highest speed position.

Using a test thermometer, check the temperature of the air being discharged at the floor outlets. Compare the test thermometer reading to the Temperature Reference chart.

Temperature Reference Chart:

If the floor outlet air temperature is insufficient, check for a faulty heater valve (perform ATC Function Test) and verify that the cooling system is operating to specifications. Both of the heater hoses should be HOT to the touch (the coolant return heater 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 cooling system connections.
- Inoperative or stuck heater water valve.
- Plugged heater core.

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

POSSIBLE LOCATIONS OR CAUSE OF INSUFFICIENT HEAT
- An obstructed cowl air intake.
- Obstructed heater system outlets.
- Heater water valve not functioning properly.

TEMPERATURE CONTROL
If outlet air temperature cannot be adjusted with the A/C-heater temperature control, one of the following could require service:
- Faulty A/C-heater control switch.
- Faulty temperature sensor.
- Faulty A/C-heater control cable or actuator.
- Faulty A/C-heater control module.