PCM Controlled Air Conditioning Diagnosis

A/C System

A/C operation is requested by the ACM using a serial data (Class 2) message to the PCM. The PCM will ground the A/C relay allowing current to flow through the A/C Compressor clutch coil. The PCM will disable or inhibit A/C compressor clutch operation during the following conditions:

^ High power steering load indicated.
^ Engine not running.
^ Engine at wide open throttle.
^ Outside temperature below approximately 4°C (40°F).
^ Certain PCM DTCs set.

The PCM will also engage the A/C compressor clutch during cranking in colder weather to prevent A/C slugging.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. Since many DTCs disable A/C clutch operation, any DTCs must be repaired and cleared before using this table.
2. An A/C Relay status of OFF indicates that the PCM is not allowing A/C clutch operation (DTCs set or low outside temp. etc.) or the HVAC is not requesting A/C operation from the PCM. To verify PCM control of the A/C clutch, use the output test for the A/C relay and command the A/C clutch ON and OFF with the ignition ON and the engine OFF Listen for the A/C clutch to engage and disengage.
4. Checking the PCMs ability to ground the A/C Compressor Clutch Control circuit.
5. Checking for an open A/C Compressor Clutch Control circuit.