Part 1 of 2

Chart C-10 (part 1 Of 2):

A/C Control Schematic:

CIRCUIT DESCRIPTION
The A/C clutch control relay is energized by the Powertrain Control Module (PCM) which provides a ground path through CKT 459 when A/C is requested. The A/C clutch is delayed 0.3 second after A/C is requested. This allows the Idle Air Control (IAC) valve to adjust engine RPM for the additional load. A/C request is received through serial data from the Instrument Panel (I/P) cluster.

The PCM will temporarily disengage the A/C clutch relay for calibrated times for one or more of the following:

^ Hot engine restart.
^ Wide Open Throttle (Throttle Position (TP) sensor over 90%).
^ Engine speed greater than 6000 RPM.
^ During IAC valve reset.

The PCM will also disable the A/C clutch relay whenever a Diagnostic Trouble Code (DTC) 66 is present.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. The PCM will only energize the A/C relay when the engine is running. This test will determine if the relay or CKT 459 is faulty.
2. Determines if the signal is reaching the PCM through CKT 66 from the A/C control panel. Signal should only be present when an A/C mode or defrost mode has been selected.
3. A/C request is received through serial data from I/P cluster.

DIAGNOSTIC AIDS
^ If complaint is insufficient cooling, the problem may be caused by an inoperative cooling fan. Refer to Chart C-12 for cooling fan diagnosis.
^ Check circuitry spliced to A/C refrigerant pressure sensor for shorts or opens. A shorted 5v reference on the Manifold Absolute Pressure (MAP) sensor circuit could cause an inoperative A/C system.
^ Check if other codes are present, and correct if necessary.
^ Check ERLS fuse and replace if necessary. If fuses continue to blow whenever A/C is requested check A/C compressor clutch diode.