A/C Request Signal

The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the temperature setting. The ECM will operate the A/C system automatically in FRONT DEFROST mode to help reduce moisture inside the vehicle. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control assembly. The A/C system maybe running without the A/C LED indicator illuminated when in FRONT DEFROST mode. The following conditions must be met in order for the ECM to turn on the compressor clutch:

1. BCM  - Battery voltage is 9-16 volts and A/C request from the HVAC control assembly.
2. ECM  - Engine Coolant Temperature (ECT) is less than 253°F (123°C), engine speed is 600-5300 RPM and A/C high side pressure is 428-44 psi (2951-310 kPa).

Once engaged, the compressor clutch will be disengaged for the following conditions:

• Throttle position is 100 percent for 10 seconds.
• A/C high side pressure is more than 428 psi (2951 kPa) and will reengage once the pressure drops below 300 psi (2068 kPa).
• A/C high side pressure is less than 44 psi (310 kPa).
• Engine Coolant Temperature (ECT) is more than 253°F (123°C).
• Engine speed is less than 475 RPM.
• Engine speed is more than 6000 RPM.
• ECM detects excessive torque load.
• ECM detects insufficient idle quality.

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