Air Conditioning (A/C) Compressor Control Circuit Diagnosis. Chevrolet PJJ 2000

For 1990-2009 cars
Engine Controls Components
A/C Controls
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Diagnosis

The following table will diagnose the PCM related circuitry for the A/C circuit. For diagnosis of the refrigerant system, refer to Diagnostic System Check - HVAC Systems - Manual in HVAC Systems - Manual.

A scan tool can be used to display the following parameters:

• | A/C Request -- This displays if the PCM has received an A/C request from instrument panel cluster (IPC) YES or NO.

• | A/C Relay -- This displays if the PCM has commanded the A/C clutch ON or OFF.

• | A/C Highside Pressure -- This displays the A/C refrigerant high side pressure in VOLTS and PSI.

### Circuit Description

The PCM receives an A/C request signal from the instrument panel cluster (IPC) over the 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 stop energizing the A/C compressor clutch relay for one or more of the following conditions:

• | A hot engine restart.

• | A wide open throttle (TP sensor over 90 percent).

• | Engine RPM of more than 6,000 RPM.

• | During an idle air control (IAC) valve reset.

| The A/C compressor clutch relay will remain deenergized 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.

| For more information on the A/C refrigerant system, refer to Diagnostic System Check - HVAC Systems - Manual in HVAC Systems - Manual.

### Diagnostic Aids

• | If DTCs P0530 or U1016 are set, do not use this table.

• | If the complaint is insufficient cooling, the cause may be an inoperative cooling fan. Refer to Electric Cooling Fan Diagnosis .

• | If the fan operates correctly, refer to Diagnostic System Check - HVAC Systems - Manual in HVAC Systems - Manual.

• | An A/C refrigerant pressure outside the range of 296.49-2951.06 kPa (43-428 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 the A/C ON. If pressure is outside of the specified range, refer to Diagnostic System Check - HVAC Systems - Manual in HVAC Systems - Manual.

### Test Description

The numbers below refer to numbers on the diagnostic table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.

2. The PCM will only energize the A/C relay when the engine is running. This test will determine if the relay or control circuit is malfunctioning.

3. By disconnecting the relay, the system can be divided into two sections. If the clutch does not disengage, the malfunction lies on the compressor side of the system.

4. A test lamp that does not illuminate indicates that the A/C compressor clutch relay is malfunctioning.

5. Determines if the system is normal or if the A/C refrigerant pressure sensor reading is out of range.

6. Determines if the signal is reaching the PCM from the A/C control panel through the IPC. The signal should only be present when an A/C mode or defrost mode has been selected.

7. The A/C request signal is communicated through the body control module (BCM) to the PCM over the Class 2 Serial Data line. The A/C selector switch must send a signal to the BCM before the BCM will send a signal to the PCM to turn ON the A/C compressor.

8. This step determines if the A/C refrigerant pressure sensor is out of range causing the A/C compressor clutch to be disabled or if the A/C charge is to low to allow A/C operation.

9. Connecting circuits 59 and 439 together bypasses the PCMs control of the A/C compressor clutch. An A/C compressor clutch that fails to engage at this point indicates that the malfunction is in circuit 59, the compressor coil or compressor coil ground circuit.

10. With the engine running and the A/C relay commanded ON, the PCM should ground the A/C relay control circuit. This will also illuminate the test lamp.

11. Before replacing the PCM, check for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminals to wiring connections or physical damaged to the wiring harness. The replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Techline™ procedure for the PCM reprogramming.

12. If no malfunctions have been found at this point, refer to Diagnostic Aids for additional checks and information.

#### A/C Compressor Clutch Control Circuit Diagnosis

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you Perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Turn ON the ignition switch leaving the engine OFF. Install a scan tool. Were DTCs P0530 or U1016 set? | -- | Go to Diagnostic Trouble Code (DTC) List/Type | Go to Step 3
3 | Is the A/C compressor clutch engaged? | -- | Go to Step 4 | Go to Step 5
4 | Remove the A/C relay. Refer to Air Conditioning (A/C) Compressor and Cooling Fan Relays Replacement . Does the A/C compressor clutch disengage? | -- | Go to Step 6 | Go to Step 7

5

1. Start the engine.
2. Allow the engine coolant temperature to reach the specified value.
3. Cycle ON and OFF the A/C selector switch.

Does the A/C compressor clutch cycle ON and OFF when the selector switch is cycled?

85°C (185°F)

Go to Step 8

Go to Step 9

6

1. Connect a test lamp to B+.
2. Probe the A/C relay control terminal with the test lamp.

Does the test lamp illuminate?

--

Go to Step 20

Go to Step 30

7 | Disconnect the A/C clutch electrical connector. Does the A/C compressor clutch disengage? | -- | Go to Step 21 | Go to Step 32

8

1. Turn OFF the ignition switch.
2. Install an A/C manifold gauge set.
3. Observe the A/C High side pressure on the scan tool and the manifold gauge set.

Are the A/C High side pressures within the specified value of each other?

138 kPa (20 psi

Go to Step 36

Go to Step 10

9 | Turn ON and OFF the A/C selector switch. Does the scan tool indicate when the A/C is requested and not requested correctly? | -- | Go to Step 11 | Go to Step 12

10

1. Disconnect the A/C refrigerant pressure sensor electrical connector.
2. Connect a DMM to B+.
3. Probe the A/C refrigerant pressure sensor ground circuit with the DMM.

Does the DMM read the specified value?

B+

Go to Step 31

Go to Step 22

11 | Turn OFF the engine leaving the ignition switch ON. Is the A/C High side value between the specified values? | 276-2965 kPa(40-430 psi) | Go to Step 13 | Go to Step 14

12

1. Connect a test lamp to ground.
2. Probe the A/C selector switch input circuit to the BCM with the test lamp.
3. Cycle ON and OFF the A/C selector switch.

Does the test lamp turn ON and OFF when the A/C selector switch is cycled?

--

Go to Step 34

Go to Step 23

13

1. Remove the A/C relay. Refer to Air Conditioning (A/C) Compressor and Cooling Fan Relays Replacement .
2. Connect a test lamp to ground.
3. Probe the following A/C relay circuits with the test lamp.

• | Ignition feed

• | Battery feed

Does the test lamp illuminate on both circuits?

--

Go to Step 15

Go to Step 24

14

1. Install an A/C manifold gauge set.
2. Observe the A/C High side pressure on the scan tool and the manifold gauge set.

Are the A/C High side pressure within the specified value of each other?

138 kPa (20 psi

Go to Diagnostic Starting Point - HVAC Systems - Manual in HVAC Systems - Manual

in HVAC System - Manual

Go to Step 31

15

Connect a fused jumper wire between the following circuits:

• | A/C relay ignition feed terminal

• | Compressor clutch feed terminal

Does the A/C compressor clutch engage?

--

Go to Step 16

Go to Step 17

16

1. Remove the fused jumper wire.
2. Start the engine.
3. with the A/C selected on, Command ON the A/C Compressor Clutch relay with scan tool.
4. Connect a test lamp to B+.
5. Probe the A/C compressor clutch relay control terminal with the test lamp.

Does the test lamp illuminate?

--

Go to Step 30

Go to Step 18

17

1. Disconnect the A/C compressor clutch electrical connector.
2. Connect a test lamp to ground.
3. Fused jumper wire still installed, probe the A/C compressor clutch ignition feed circuit with the test lamp.

Does the test lamp illuminate?

--

Go to Step 19

Go to Step 26

18

1. Turn the ignition ON, with the engine OFF.
2. Connect the test lamp to ground.
3. Probe the compressor clutch relay control terminal with the test lamp.

Did the test lamp illuminate?

--

Go to Step 27

Go to Step 28

19

1. Connect a test lamp to B+.
2. Probe the A/C compressor clutch ground circuit with the test lamp.

Does the test lamp illuminate?

--

Go to Step 33

Go to Step 29

20

1. Check the A/C compressor clutch relay control circuit for a short to ground.
2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 36

Go to Step 35

21 | Repair the short to B+ in the A/C compressor clutch ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 36 | --

22

1. Check the A/C refrigerant pressure sensor ground for the following conditions:

• | Open circuit

• | Poor electrical terminal connection at the PCM

2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 36

Go to Step 35

23 | Repair the signal from the A/C selector switch. Did you complete the repair? | -- | Go to Step 36 | --

24

If the test lamp did not illuminate on the A/C relay battery feed terminal or the ignition feed, check for a short to ground in the following items:

• | A/C compressor clutch ignition feed circuit

• | A/C compressor clutch diode

• | Battery feed circuit

• | Ignition feed circuit

Did you find and correct the condition?

--

Go to Step 36

Go to Step 25

25

1. Turn OFF the ignition Switch.
2. Check for an open circuit or the following conditions in the A/C Compressor Clutch relay in the following circuits:

• | Battery feed

• | Ignition feed

• | Open fuses

• | Poor electrical terminal connection at the fuses

3. Repair the circuits as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 36

Go to Step 30

26

1. Turn OFF the ignition switch.
2. Repair the open in the A/C compressor clutch ignition feed circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 36

--

27

1. Check the A/C compressor clutch relay control circuit for a short to voltage.
2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 36

Go to Step 35

28

1. Check the A/C compressor clutch relay control circuit for the following conditions:

• | Open circuit

• | Poor electrical terminal connection at the PCM

2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and corect the condition?

--

Go to Step 36

Go to Step 35

29

1. Check the A/C compressor clutch ground circuit for the following conditions:

• | Open circuit

• | Poor electrical terminal connections

2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 36

--

30

1. Turn OFF the ignition switch.
2. Check for poor electrical terminal connections at the A/C relay. Repair the connections as necessary. Refer to Wiring Repairs in Wiring Systems.
3. If the electrical terminal connections are OK, then replace the A/C compressor clutch relay. Refer to Air Conditioning (A/C) Compressor and Cooling Fan Relays Replacement .

Did you complete the repair?

--

Go to Step 36

--

31

1. Check for poor electrical terminal connections at the A/C refrigerant pressure sensor electrical connector. Repair the connections as necessary. Refer to Wiring Repairs in Wiring Systems.
2. If the electrical terminal connections are OK, then replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in HVAC Systems - Manual.

Did you complete the repair?

--

Go to Step 36

--

32 | Replace the malfunctioning A/C compressor clutch assembly. Refer to Compressor Clutch Plate/Hub Assembly Install in HVAC Systems - Manual. Did you complete the replacement? | -- | Go to Step 36 | --

33

1. Turn OFF the ignition switch.
2. Check for a poor electrical terminal connections at the A/C compressor clutch coil. Repair the connections as necessary. Refer to Wiring Repairs in Wiring Systems.
3. If the electrical terminal connections are OK, then replace the A/C compressor clutch coil. Refer to Compressor Clutch Plate/Hub Assembly Install in HVAC Systems - Manual

Did you complete the repair?

--

Go to Step 36

--

34 | Refer to Diagnostic System Check - Body Control System in Body Control System. Did you find and correct the condition? | -- | Go to Step 36 | --

35

1. Turn OFF the ignition switch.

Important: The replacement PCM must be programmed.

2. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Did you complete the replacement?

--

Go to Step 36

--

36

1. Start the engine.
2. Idle the engine.
3. Cycle ON and OFF the A/C selector switch.

Does the A/C compressor clutch cycle ON and OFF?

System OK

Go to Step 2