Dakota R/T 2WD V8-5.9L VIN Z LDC (1999)
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 in put 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 powertrain control module (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 idle air control (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.
