Grand Cherokee 2WD L6-4.0L VIN S (1997)
A/C Signal: Description and Operation
AIR CONDITIONING (A/C) CONTROLS-PCM INPUT
The A/C control system information applies to factory installed air conditioning units.
A/C SELECT SIGNAL:
When the A/C switch is in the ON position, an input signal is sent to the Powertrain Control Module (PCM). The signal informs the PCM that the
A/C has been selected. The PCM adjusts idle speed to a pre-programmed rpm through the Idle Air Control (IAC) motor to compensate for
increased engine load.
A/C REQUEST SIGNAL:
Once A/C has been selected, the PCM receives the A/C request signal from the clutch cycling pressure switch. The input indicates that the
evaporator pressure is in the proper range for A/C application. The PCM uses this input to cycle the A/C compressor clutch (through the A/C
relay). It will also determine the correct engine idle speed through the IAC motor position.
If the A/C low-pressure switch or high-pressure switch opens (indicating a low or high refrigerant pressure), the PCM will not receive an A/C
request signal. The PCM will then remove the ground from the A/C relay. This will deactivate the A/C compressor clutch.
If the switch opens, (indicating that evaporator is not in proper pressure range), the PCM will not receive the A/C request signal. The PCM will
then remove the ground from the A/C relay deactivating the A/C compressor clutch.
