A/C Request Signal

The A/C system can be engaged by either pressing the A/C switch or during automatic operation. The Instrument Panel Module (IPM) receives a request input from the HVAC control module. The HVAC system uses a scroll compressor that incorporates a thermal switch that opens once the compressor temperature is more than 311°F (155°C). In order for the PCM to internally ground the A/C compressor clutch relay control circuit, the Dash Integration Module (DIM) and the PCM must communicate to each other over the Class 2 serial data circuits.

The PCM monitors A/C refrigerant line pressure and engine coolant temperature. The DIM monitors A/C refrigerant line pressure, A/C refrigerant temperature, engine coolant temperature, battery voltage and A/C request from the IPM.

The DIM will request A/C operation from the PCM if these parameters are within normal operating limits and the ambient temperature is more than 37°F (3°C). If the A/C compressor is turned off due to low ambient temperatures, the A/C compressor will not be turned back on until the ambient temperature reaches 42°F (6°C). Once engaged, the compressor clutch will be disengaged for the following conditions:

• Compressor thermal switch is opened.
• Throttle position is 100 percent.
• A/C Pressure is more than 430 psi (2968 kPa).
• A/C Pressure is less than 35 psi (255 kPa).
• Engine coolant temperature is more than 259°F (121°C).
• Evaporator temperature.
• Engine speed is more than 5000 RPM.
• Transmission shift.
• PCM detects excessive torque load.
• PCM detects insufficient idle quality.
• PCM detects a hard launch condition.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.