Powertrain Control Module (PCM) receives an A/C request signal from Body Control Module (BCM) over Class 2 serial data line. When A/C is requested, PCM provides a ground path to A/C clutch relay control circuit. When relay circuit is grounded, A/C clutch relay is energized. The PCM delays grounding relay circuit for.3 seconds. This allows PCM to adjust engine idle RPM for additional load.
The PCM will disengage A/C compressor clutch if one or more of the following conditions occur:
Throttle angle is greater than 90 percent.
A/C head pressure is greater than 440 psi (31 kg/cm2 ) with A/C refrigerant pressure sensor reading greater than 4.27 volts.
A/C head pressure is less than 35 psi (2.5 kg/cm2 ) with A/C refrigerant pressure sensor reading greater than.40 volts.
Ignition voltage is less than 10.5 volts.
Engine speed is greater than 4300 RPM for 5 seconds or at 5400 RPM for any amount of time.
Engine coolant temperature is greater than 255 Â F (124 Â C).
Intake air temperature is less than 41 Â F (5 Â C).
Monday, March 29th, 2010 AT 7:29 PM