Normal Operation

WARNING: This page is about a different car, the 2007 Lincoln Mark LT and 2007 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.

Under normal operation, when A/C is requested, a message is sent over the UART-based protocol (UBP) bus to the instrument cluster, then from the instrument cluster through the controller area network (CAN) bus to the PCM (HVAC module - electronic automatic temperature control [EATC] systems) or sends voltage to the instrument cluster through circuit 348 (VT) then a message from the instrument cluster through the CAN bus to the PCM (HVAC module - electronic manual temperature control [EMTC] systems). Voltage is provided to the A/C cycling switch through circuit 295 (LB/PK). The PCM receives input from the A/C cycling switch through circuit 347 (BK/YE).

The PCM provides a ground for the A/C clutch relay coil through circuit 331 (PK/YE). The A/C clutch relay coil receives ignition voltage through circuit 391 (RD/YE). Ignition voltage for the A/C clutch relay switch is provided through circuit 883 (PK/LB). When the relay is activated, ignition voltage is supplied to the A/C clutch solenoid through circuit 321 (GY/WH). Ground is supplied for the A/C clutch through circuit 57 (BK).

This pinpoint test is intended to diagnose the following:

Wiring, terminals or connectors
PCM
HVAC module - EATC
HVAC module - EMTC
A/C compressor clutch field coil
A/C control relay
A/C clutch air gap