Symptom Related Diagnostic Procedures

NOTE: The air handling system is designed to provide Defrost when no vacuum is applied to any of the three vacuum control motors. This is done to prevent a situation where Defrost cannot be obtained due to a system vacuum leak. Instead, a leak in the vacuum control circuit will send all air flow to the defroster outlets. This condition may occur during acceleration (slow vacuum leak), may exist at all times (large vacuum leak) and may happen only when certain specific functions are selected, indicating a leak in that portion of the circuit.

NOTE: 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. Because of the materials used, the vacuum hoses should never be pinched off during diagnosis to locate a leak. Use Rotunda Vacuum Tester or equivalent to locate vacuum leaks. 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.

NOTE: Use Rotunda 73 Digital Multimeter or equivalent for diagnosis of the following pinpoint tests.