For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
1 | Start the engine. Select the DEFROST mode. Select the maximum blower speed. Does sufficient air flow from the defroster outlets? | Go to Step 2 | Go to Step 9
2 | Measure the engine operating temperature. Does engine reach a normal operating temperature? | Go to Step 3 | Go to Step 4
3 |

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 11

4 | 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 13 | --
5 | Test the operation of the A/C compressor clutch. Does the A/C compressor clutch engage? | Go to Step 7 | Go to Step 6
6 | Repair the A/C compressor clutch. Refer to HVAC Compressor Clutch Does Not Engage in HVAC Systems-Manual. Is the repair complete? | Go to Step 13 | --
7 | Perform the A/C system performance test. Refer to Air Conditioning (A/C) System Performance Test . Is the A/C system operating within the specifications? | Go to Step 8 | Go to Step 10
8 | Inspect for correct operation of the recirculation door. Is the recirculation door operating correctly? | Go to Step 13 | Go to Step 12
9 | Repair the air delivery concern. Refer to Air Delivery Improper in HVAC Systems - Manual. Is the repair complete? | Go to Step 13 | --
10 | Repair the A/C performance concern. Refer to Symptoms - HVAC Systems - Manual in HVAC Systems-Manual. Is the repair complete? | Go to Step 13 | --
11 | Repair the heating concern. Refer to Heating Performance Diagnostic . Is the repair complete? | Go to Step 13 | --
12 | Repair the recirculation door concern. Refer to Air Recirculation Malfunction in HVAC Systems - Manual. Is the repair complete? | Go to Step 13 | --
13 | Operate the system in order to verify the repair. Does the system operate correctly? | System OK | Go to Step 1