HOLDEN GEN III V8, Service Training

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GEN III V8 ENGINE MANAGEMENT
A/C REQUEST SIGNAL AND A/C CONTROL WITHOUT ECC
The BCM requests the PCM to turn the A/C compressor clutch on or off via the PIM and the serial data bus
normal mode message. The BCM monitors the voltage at terminal D9 to determine the status of the momentary
A/C master switch. When the A/C master switch is pressed, 12 volts is applied to terminal D9 via circuit 248
(Red/White wire), causing the voltage at D9 to be pulled high, 1 2 volts. The BCM sees this high voltage as an
A/C master switch input signal.
On receiving this A/C master switch input signal, the BCM will request the PCM to energise the A/C clutch via
the PIM and the serial data bus normal mode message, if the ignition is on and the blower motor is operating. If
the A/C master switch is pressed again the BCM will request the PCM to turn off the A/C compressor.
The operating status of the system will be remembered by the BCM, when the ignition is switched from on to off
or when the blower is switched off. If the blower is off and the A/C master switch is pressed, then the next time
the blower is switched on the air conditioning will be turned on. Turning the ignition off will cancel this button
press function.
The system will reset to off when the battery is disconnected.
The PCM uses this signal to:
1. Adjust the Idle Air Control (IAC) position to compensate for the additional load placed on the engine by the
air conditioning compressor, and then
2. Energise the A/C compressor relay, to operate the A/C compressor if the pressure in the A/C system is
within the correct operating range.
The PCM monitors the A/C pressure transducer to determine A/C system pressures.
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