With CJ2

Circuit Description
The CJ2 A/C system (automatic A/C), requests A/C operation via a Class 2 serial data message sent from the HVAC control head to the PCM.

The A/C clutch relay is PCM controlled. The PCM will engage the A/C clutch any time A/C has been requested unless any of the following conditions exist:
^ High coolant temperature.
^ Low A/C system pressure.
^ High A/C system pressure.
^ Wide open Throttle.
^ High engine RPM.
^ Certain DTCs are set.

When the heater and A/C control is placed in the A/C mode, a Class 2 Serial Data message is sent to the PCM requesting A/C operation. This is shown on the scan tool as A/C Request Yes. The PCM will then ground the A/C clutch relay control circuit to energize the A/C relay (if none of the above conditions exist).

When the relay is energized, the relay contacts close, and current flows through the relay to the A/C compressor clutch.

When A/C request has been detected by the PCM, the cooling fan(s) will be turned On when A/C pressure reaches a predetermined pressure.

Important: The wired A/C Request circuit may be present at the PCM connector. This wire is not used with the CJ2 HVAC system and there is no failure mode of this circuit that affects system operation.

Diagnostic Aids
Before using this table, be sure no PCM DTC(s) are stored. The PCM may not activate the A/C clutch if certain DTCs are stored.