Normal Operation

Under normal operation, when A/C is requested, a message is sent from the HVAC module over the Medium Speed Controller Area Network (MS-CAN) bus to the PCM. Ignition voltage is provided to the A/C clutch relay switch through circuit SBB24 (VT/RD). When the PCM energizes the relay, ignition voltage is supplied to the A/C clutch through circuit CH421 (GY). Ground is supplied for the A/C clutch through circuit GD120 (BK/GN).

This pinpoint test is intended to diagnose the following:

• Fuse(s)
• Wiring, terminals or connectors
• PCM
• HVAC module - Dual Automatic Temperature Control (DATC)
• HVAC module - Electronic Manual Temperature Control (EMTC)
• A/C evaporator discharge temperature sensor
• A/C pressure transducer
• A/C compressor clutch field coil
• A/C control relay
• A/C clutch air gap