Before beginning service of the HVAC system, perform the functional test. In order to obtain accurate test results, ensure that the thermostat is fully open.

1. Start the engine and warm-up to normal operating temperature.
2. Touch the upper radiator hose. The hose should feel hot to the touch, indicating that the thermostat is open.
3. Set the fresh/recirc lever to FRESH.
4. Set the temperature lever to full COLD (left).
5. Set the blower speed to HI.
6. Systematically move the mode lever through the lever's various positions. Note which vents the air flows from at each setting. In the bi-level mode, the air should come from the instrument panel (IP) vents and from the floor vents. In the defroster mode, most of the air should be directed at the windshield, with some of the air directed at the floor vent and so on.
7. Using the symbols above each mode lever position, verify that the air flows from the corresponding points. The air entering the passenger compartment should be approximately the same temperature as the temperature outside the vehicle.
8. Set the temperature lever to full HOT (right). The temperature of the air entering the passenger compartment should now be much warmer than the air outside the vehicle.
9. Systematically move the mode lever through the lever's various positions. Note which vents that the air flows from at each setting.
10. Gradually move the blower speed lever from HI to LOW. The forcefulness of the airflow should decrease at each successive setting. The blower noise should decrease at each successive setting.

If the functional test indicates an improper air delivery or a failure to shift modes when the mode lever is moved, refer to the appropriate diagnostic symptom table(s) for the proper diagnosis.