RAM 2500 Truck 4WD L6-5.9L DSL Turbo VIN 6 (1999)
Compressor Clutch Relay: Description and Operation
A/C Compressor Clutch Relay-PCM Output
AIR CONDITIONING (A/C) CLUTCH RELAY - PCM OUTPUT
Power Distribution Center (PDC)
The A/C relay is located in the Power Distribution Center (PDC). Refer to label on PDC cover for relay location.
The powertrain control module (PCM) activates the A/C compressor through the A/C clutch relay. The PCM regulates A/C compressor operation
by switching the ground circuit for the A/C clutch relay on and off.
When the PCM receives a request for A/C, it will adjust idle air control (IAC) motor position. This is done to increase idle speed. The PCM will
then activate the A/C clutch through the A/C clutch relay. The PCM adjusts idle air control (IAC) stepper motor position to compensate for
increased engine load from the A/C compressor.
By switching the ground path for the relay on and oft, the PCM is able to cycle the A/C compressor clutch. This is based on changes in engine
operating conditions. If, during A/C operation, the PCM senses low idle speeds or a wide open throttle condition, it will de-energize the relay. This
prevents A/C clutch engagement. The relay will remain de-energized until the idle speed increases or the wide open throttle condition exceeds 15
seconds or no longer exists. The PCM will also de-energize the relay if coolant temperature exceeds 125 °C (257 °F) or low or high system
pressure exists.
