A/C Compressor Control Circuit Diagnosis

Diagnostic Chart (Part 1 Of 4):

Diagnostic Chart (Part 2 Of 4):

Diagnostic Chart (Part 3 Of 4):

Diagnostic Chart (Part 4 Of 4):

Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) receives an A/C request signal from the Body Control Module (BCM). When A/C is requested, the Powertrain Control Module (PCM) provides a ground path to the A/C clutch relay control circuit. When the relay circuit is grounded, the A/C compressor clutch relay is energized. The PCM delays grounding the relay circuit for 0.3 second, so the PCM can adjust the engine idle RPM for the additional load.

The PCM will temporarily de-energize the A/C compressor clutch relay for one or more of the following conditions:
^ A hot engine restart
^ A wide open throttle, where the throttle sensor (TP) position is more than 90 percent
^ An engine RPM more than 6,000 RPM

During an Idle Air Control (IAC) valve reset, the A/C compressor clutch relay will remain de-energized when one or both of the following conditions exist:
^ A DTCs P0530 or U1016 is set.
^ There is no A/C request signal to the PCM. Refer to A Diagnostic System Check - HVAC Systems - Manual in Healing, Ventilation, and Air Conditioning for more information on the A/C refrigerant systems. Initial Inspection and Diagnostic Overview

DIAGNOSIS
The following table will diagnose the PCM-related circuitry of the A/C circuit. Refer to A Diagnostic System Check - HVAC Systems - Manual Heating, Ventilation, and Air Conditioning for diagnosis of the refrigerant portion of the system. Initial Inspection and Diagnostic Overview

A scan tool can be used to display the following parameters:
^ An A/C Request - This displays if PCM has received an A/C request from Instrument Panel Cluster (IPC) YES or NO.
^ The A/C Relay - This displays if the PCM has commanded the A/C clutch ON or OFF.
^ The A/C High Side Pressure This displays the A/C refrigerant high side pressure in VOLTS and pounds Per Square Inch (PSI).

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) receives an A/C request signal from the Instrument Panel Cluster (IPC) over the Universal Asynchronous Receiving/Transmitting (UART) serial data line. When A/C is requested, the Powertrain Control Module (PCM) provides a ground path to the A/C clutch relay control circuit. When the relay circuit is grounded, the A/C compressor clutch relay is energized. The PCM delays grounding the relay circuit for 0.3 second, so the PCM can adjust the engine idle RPM for the additional load.

The PCM will temporarily de-energize the A/C compressor clutch relay for one or more of the following conditions:
^ A hot engine restart
^ A wide-open throttle, where the throttle position (TP) sensor is more than 90 percent.
^ An engine RPM more than 6,000 RPM During an Idle Air Control (IAC) valve refer the A/C compressor clutch relay will remain de-energized when one or both of the following conditions exist:
^ A DTC P0530 or U1016 is set.
^ There is no A/C request signal to the PCM. Refer to A Diagnostic System Check - HVAC Systems - Manual in Heating, Ventilation and Air Conditioning. Initial Inspection and Diagnostic Overview

DIAGNOSTIC AIDS
^ If DTCs P0530 or U1016 are set, do not use this table.
^ If the complaint is insufficient cooling, the problem may be caused by an inoperative cooling fan. Refer to Electric Cooling Fan Diagnosis. Component Tests and General Diagnostics
^ If the fan operates correctly, refer to Function Test in Heating, Ventilation and Air Conditioning. Function Test
^ An A/C refrigerant pressure outside the range of 43 to 428 psi will cause the A/C compressor clutch to be disabled by the PCM. Observe the A/C refrigerant pressure parameter on the scan tool for 2 minutes with the engine idling and A/C ON. If pressure goes out of range, refer to cooling Insufficient, A/C System in Heating, Ventilation and Air Conditioning. Symptom Related Diagnostic Procedures

TEST DESCRIPTION
The numbers below refer to the steps on the diagnostic table.
3. This step tests if the A/C compressor clutch is engaged when there is no command to be engaged.
4. This step tests if the A/C compressor clutch is functioning. If the A/C clutch operates, inspect for faulty connections throughout the system.
8. The A/C clutch relay is located in the underhood electrical center. This step tests the PCM and the A/C clutch relay control circuit.
13. There should be no A/C request when the HVAC control module OFF.
14. The A/C request circuit is shorted to a voltage between the A/C high pressure switch and the PCM if the scan tool indicates an A/C request when the switch is disconnected.
18. This step tests for a short to ground on the A/C relay control circuit.
19. This step tests for a short between the A/C relay control circuit and any other circuit in the PCM harness connector.