A/C Request Signal

The A/C system is engaged by selecting any switch on the HVAC Control Module (IPM) except the A/C OFF switch. The A/C switch will illuminate A/C OFF when the A/C switch is selected. The IPM sends a class 2 A/C request message to the Powertrain Control Module (PCM) for A/C compressor clutch operation. The Dash Integration Module (DIM) must communicate with the PCM in order for the A/C clutch to be engaged. The HVAC system uses a scroll compressor that incorporates a thermal switch that opens once the compressor temperature is more than 257°F (125°C). The following conditions must be met for the PCM to turn on the compressor clutch from the IPM request:

• DIM will allow A/C operation if the A/C line pressure sensor, A/C refrigerant low temperature sensor, Engine Coolant Temperature (ECT) sensor, and battery voltage limits are all within normal operating range.
• IPM will allow A/C operation if the evaporator temperature sensor is more than 39°F (4°C) and the control module operating range is 9-16 volts.
• PCM will allow A/C operation if the ECT is less than 262°F (128°C), engine speed is more than zero RPM and A/C pressure is between 413 psi (2850 kPa) and 30 psi (204 kPa).

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 413 psi (2850 kPa)
• A/C Pressure is less than 30 psi (204 kPa)
• ECT is more than 262°F (128°C)

If there is a malfunction in the A/C system, the Driver Information Center (DIC) display will read SERVICE A/C SYSTEM to alert the driver. When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.