Heater Performance Test

Be certain that the accessory vacuum supply line is connected at the engine intake manifold.

Temperature Reference:

MAXIMUM HEATER OUTPUT
Engine coolant is delivered to the heater core through two heater hoses. With the engine idling at normal operating temperature, set the temperature control knob in the full hot position, the mode control switch knob in the floor heat position, and the blower motor switch knob in the highest speed position. Using a test thermometer, check the temperature of the air being discharged at the heater-A/C housing floor outlets. Compare the test thermometer reading to the Temperature Reference chart.

TEMPERATURE CONTROL
If the heater outlet air temperature cannot be adjusted with the temperature control knob on the heater-A/C control panel, the following could require service:
- The heater-A/C control.
- The temperature control assembly in the control head.
- The electric blend-air door motor.
- Any associated wiring harness or connectors.
- The blend-air door.
- Improper engine coolant temperature.