PCM Controlled A/C Circuit Diagnosis
CIRCUIT DESCRIPTIONThe PCM uses the A/C relay to control the A/C compressor. With an A/C mode selected, the Instrument Panel Module (IPM) sends a class 2 message to the Dash Integration Module (DIM). The DIM checks to ensure that the conditions are right to allow the operation of the compressor. If the conditions are right, the DIM sends the A/C Request to the PCM via class 2 serial data. When the PCM receives the message, the PCM turns ON the A/C relay coil by grounding the A/C relay control circuit. This closes the relay contacts, and applies a fused battery voltage to the A/C compressor clutch coil. The PCM enables the compressor clutch whenever following conditions are present:
^ Engine is running.
^ The PCM has received the A/C request from the DIM.
The DIM monitors the following components to decide whether or not to send the A/C Request:
- A/C pressure
- Low side pressure
- System voltage
- Engine coolant
^ TP sensor indicates a throttle angle below 90 percent.
^ System voltage more than 8 volts.
^ Engine speed is more than 500 RPM.
DIAGNOSTIC AIDS
Check for the following conditions:
^ Faulty connections at the PCM and A/C compressor.
Inspect the harness connectors for the following conditions:
^ Backed out terminals
^ Improperly mated terminals
^ Broken locks
^ Improperly formed or damaged terminals
^ Faulty terminal to wire connections
Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ A damaged harness.
Inspect the wiring harnesses for damage and repair as necessary. Refer to Wiring Repairs in Diagrams.
TEST DESCRIPTION
