1. Start the engine.
2. Select the DEFROST mode.
3. Select the maximum blower speed.

Does sufficient air flow from the defroster outlets?

Go to Step 2

Go to Step 5

Measure the engine operating temperature.

Does engine reach a normal operating temperature?

Go to Step 3

Go to Step 4

1. Select the minimum blower speed.
2. Select the maximum temperature setting.
3. Feel the temperature of the inlet and outlet hoses at the heater core.

Does the inlet hose feel warmer than the outlet hose?

Go to Step 5

Go to Step 6

Repair the low engine temperature concern. Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling.

Is the repair complete?

Go to Step 7

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Repair the air delivery concern. Refer to Air Delivery Improper in HVAC Systems - Manual.

Is the repair complete?

Go to Step 7

--

Repair the heating concern. Refer to Heating Performance Diagnostic .

Is the repair complete?

Go to Step 7

--

Operate the system in order to verify the repair.

Does the system operate correctly?

System OK

Go to Step 1