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 Diagnostic System Check - HVAC Systems - Manual in Heating, Ventilation, and Air Conditioning for more information on the A/C refrigerant systems.
Diagnosis
The following table will diagnose the PCM-related circuitry of the A/C circuit. Refer to Diagnostic System Check - HVAC Systems - Manual in Heating, Ventilation, and Air Conditioning for diagnosis of the refrigerant portion of the system.
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 Diagnostic System Check - HVAC Systems - Manual in Heating, Ventilation and Air Conditioning.
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 . |
| • | If the fan operates correctly, refer to Function Test in Heating, Ventilation and Air Conditioning. |
| • | 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 - Air Conditioning (A/C) System in Heating, Ventilation and Air Conditioning. |
Test Description
The numbers below refer to the steps on the diagnostic table.
-
This step tests if the A/C compressor clutch is engaged when there is no command to be engaged.
-
This step tests if the A/C compressor clutch is functioning. If the A/C clutch operates, inspect for faulty connections throughout the system.
-
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.
-
There should be no A/C request when the HVAC control module OFF.
-
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.
-
This step tests for a short to ground on the A/C relay control circuit.
-
This step tests for a short between the A/C relay control circuit and any other circuit in the PCM harness connector.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||
2 | Install a scan tool. Turn ON the ignition, leaving the engine OFF. Was DTC P0530 set? | -- | Go to DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit . | |||||||||||
|
Important: This diagnostic table assumes the following:
Is the A/C compressor clutch engaged? | -- | |||||||||||||
Does the A/C compressor clutch engage? | -- | System OK | ||||||||||||
5 | Inspect both A/C clutch relay fuses for being open. Are both fuses for the A/C clutch relay OK? | -- | ||||||||||||
6 | Monitor the A/C Request using a scan tool. Does the scan tool display A/C Request as YES? | -- | ||||||||||||
7 | Is the HVAC fuse open? | -- | ||||||||||||
Does the test lamp turn ON and OFF when commanded? | -- | |||||||||||||
9 | Probe both A/C clutch relay B+ supply circuits at the underhood electrical center using the test lamp connected to a ground. Does the test lamp illuminate for both B+ circuits? | -- | ||||||||||||
10 | Jumper the A/C clutch circuit to the B+ circuit using a fuse jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems. Does the A/C clutch engage? | -- | ||||||||||||
11 |
Does the test lamp illuminate? | -- | ||||||||||||
12 | Connect the test lamp across the A/C clutch harness connector. Does the test lamp illuminate? | -- | ||||||||||||
Monitor the A/C Request using a scan tool. Does the scan tool display A/C Request as YES? | -- | |||||||||||||
Does the est lamp illuminate? | -- | |||||||||||||
15 |
Is the resistance within the specified range? | 0-2ohms | ||||||||||||
16 | Disconnect the A/C clutch relay from the underhood electrical center. Does the A/C clutch disengage? | -- | ||||||||||||
17 | Probe the A/C clutch relay control circuit at the underhood electrical center using the test lamp connected to B+. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | -- | ||||||||||||
Does the test lamp illuminate? | -- | |||||||||||||
Test continuity from the A/C clutch control circuit to all other circuits in the PCM harness connector using the DMM. Refer to Testing for Continuity in Wiring Systems. Do any of the circuits display a resistance within the specified range? | 0-2ohms | |||||||||||||
20 | Is the A/C fuse open? | -- | ||||||||||||
21 |
Does the test lamp illuminate? | -- | ||||||||||||
22 |
Does the test lamp illuminate? | -- | Go to Clutch Rotor and/or Bearing Removal in HVAC Systems. | |||||||||||
23 |
Does the DMM display continuity? | -- | ||||||||||||
24 | Repair the open circuit for the circuit that did not illuminate the test lamp. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
25 | Repair the open A/C clutch circuit between the relay and the clutch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
26 |
Did you find and correct the condition? | -- | System OK | Go to Clutch Rotor and/or Bearing Removal in HVAC Systems. | ||||||||||
27 | Repair the open A/C clutch ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
28 | Replace the HVAC control head. Refer to Control Assembly Replacement in HVAC Systems-Manual. Is the action complete? | -- | System OK | -- | ||||||||||
29 | Repair the short to voltage between the A/C clutch relay and the A/C compressor clutch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
30 | Repair the short to ground between the A/C clutch relay and the A/C compressor clutch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
31 | Replace the A/C clutch relay. Is the action complete? | -- | System OK | -- | ||||||||||
32 | Repair the grounded A/C clutch relay control circuit between the PCM and the A/C clutch relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
33 | Repair the short between the A/C clutch relay control circuit and the circuit that had continuity. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
34 | Repair the open A/C request circuit between the PCM and the HVAC control head switch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
35 | Repair the A/C request circuit for a short to ground. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
36 | Repair the A/C request circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
37 | Repair the grounded IGN E circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
38 | Repair the grounded circuit between the A/C clutch and A/C compressor clutch relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
39 |
Did you find and correct the condition? | -- | System OK | |||||||||||
40 |
Important: Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | System OK | -- | ||||||||||
41 | Repair the open A/C Clutch relay control circuit between the underhood electrical center and the PCM. Is the action complete? | -- | System OK | -- |
