Wrangler 4WD L4-150 2.5L VIN P MFI (1998)
Powertrain Control Module: Description and Operation
(A/C) Controls-PCM Input
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 powertrain control module (PCM) receives the A/C request signal from the evaporator
switch. The input indicates that the evaporator temperature 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 opens (indicating a low refrigerant level), the PCM will not receive an A/C receive signal. The PCM will then remove
the ground from the A/C relay. This will deactivate the A/C compressor clutch.
If the evaporator switch opens, (indicating that evaporator is not in proper temperature 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.
(ASD) Relay Sense-PCM Input
AUTOMATIC SHUTDOWN (ASD) RELAY SENSE-PCM INPUT
Fig. 2 Power Distribution Center (PDC)
A 12 volt signal at this input indicates to the powertrain control module (PCM) that the Automatic Shutdown (ASD) has been activated. The ASD
relay is located in the Power Distribution Center (PDC). The PDC is located in the engine compartment (Fig. 2). Refer to label on PDC cover for
relay location. The ASD relay is used to connect the oxygen sensor heater elements, ignition coil, and fuel injectors to the 12 volt + power supply.
Jeep models of previous years had used the ASD relay to apply the 12 volt + power supply to the generator field source (+) circuit. This generator
circuit is now supplied 12 volts + directly from the PCM.
This input is used only to sense that the ASD relay is energized. If the PCM does not see 12 volts at this input when the ASD should be activated,
it will set a Diagnostic Trouble Code (DTC).
Air Conditioning (A/C) Clutch Relay-PCM Output
AIR CONDITIONING (A/C) CLUTCH RELAY-PCM OUTPUT
