Verify the customer's concern by operating the climate control system to duplicate the condition.
Inspect to determine if one of the mechanical or electrical concerns apply:
Visual Inspection Chart
VISUAL INSPECTION CHART [a]: A leak in the vacuum control circuit will send all airflow to the defroster outlets. This condition may occur during acceleration (slow leak), may exist at all times (large leak), and may exist only when specific functions are selected (indicating a leak in that portion of the circuit). The vacuum hoses used in the passenger compartment control circuit are constructed from PVC plastic material. The vacuum hoses used in the engine compartment are constructed of Hytrel(R). Because of the materials used, never pinch the vacuum hoses off during diagnosis to locate a leak. A wood golf tee can be used as a plug when it is necessary to plug one end of a vacuum hose for leak test purposes.
If the inspection reveals obvious concerns that can be readily identified, repair as necessary.
If the concern remains after the inspection, connect the scan tool to the Data Link Connector (DLC) located beneath the instrument panel and select the vehicle to be tested from the scan tool menu. If the scan tool does not communicate with the vehicle:
check that the program card is correctly installed.
check the connections to the vehicle.
check the ignition switch position.
If the scan tool still does not communicate with the vehicle, refer to the scan tool manual.
Carry out the DATA LINK DIAGNOSTIC TEST using the scan tool. If the scan tool responds with:
CKT 914 and CKT 915 = All module NO RESP/NOT EQUIP, go to Communication System Diagnostics in Module Communication Network (Information Bus) to diagnose network concern.
If the Powertrain Control Module (PCM) is not listed for a communication concern, turn the A/C function selector switch to OFF and execute Self-Test Diagnostics for PCM.