Compressor Clutch Control Circuit Diagnosis

If On-Board Diagnostic (OBD) System Check has not been performed, see the BASIC TESTING article and go to OBD SYSTEM CHECK. If OBD SYSTEM CHECK has been performed, go to next step.
Check for any DTCs that may be set. If any DTCs are set, perform diagnosis for that DTC first. See the TESTS W/CODES article. If no DTCs are set, go to next step.
Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). Turn A/C off. Start engine and let idle. Observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 21). If A/C compressor clutch is not engaged, go to next step.
Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on A/C control head. Observe A/C compressor clutch. If A/C compressor clutch is engaged, system is operating correctly. Problem may be intermittent. If A/C compressor clutch is not engaged, go to next step.
With DEFROST or MAX mode still selected, observe A/C REQUEST display on scan tool. If A/C REQUEST displays YES, go to step 9). If A/C REQUEST does not display YES, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. With DEFROST or MAX mode still selected, use a voltmeter and measure voltage on A/C request circuit (Dark Green/White wire) at PCM harness connector. If reading is near battery voltage, go to step 8). If reading is not as specified, go to next step.
Check A/C request circuit (Dark Green/White wire) for an open, short to ground, or poor connection at A/C control head. Repair as necessary. Go to step 37). If no problem is found, diagnose A/C controls.
Check A/C request circuit (Dark Green/White wire) for a poor connection at PCM. Repair as necessary. Go to step 37). If no problem is found, go to step 35).
Observe A/C refrigerant pressure sensor display on scan tool. If reading is .35-4.27 volts, go to step 12). If reading is not as specified, go to next step.
Install A/C manifold gauge set. Observe high-side refrigerant pressure on gauge. If high-side refrigerant pressure is 34-414 psi (2.3-29 kg/cm² ), go to next step. If high-side refrigerant pressure is not as specified, charge A/C system using approved A/C refrigerant recovery/recycling equipment. Go to step 37).
Turn ignition off. Disconnect PCM and A/C refrigerant pressure sensor. Using an ohmmeter, measure resistance of following circuits between PCM and A/C refrigerant pressure sensor harness connectors:
- Refrigerant pressure sensor signal circuit (Red/Black wire).
- 5-volt reference "B" circuit (Gray wire).
- Sensor ground circuit (Black wire).
If any resistance is greater than 5 ohms, locate and repair cause of high resistance in circuit as necessary, then go to step 37). If any resistance is not greater than 5 ohms, go to step 18).
Disconnect A/C relay harness connector. Using a test light connected to ground, probe ignition feed circuits (Pink wires) at A/C relay harness connector. If test light comes on, go to next step. If test light does not come on, go to step 31).
Connect a fused jumper between ignition feed circuit and A/C compressor clutch ignition feed circuit (Dark Green wire) at A/C relay connector. If A/C compressor clutch engages, go to step 14). If A/C compressor clutch does not engage, leave jumper wire in place and go to step 15).
Check for poor connections at A/C relay. Repair as necessary. Go to step 37). If no problem is found, go to step 32).
Disconnect A/C compressor clutch harness connector. Connect a test light between A/C compressor clutch ignition feed circuit (Dark Green wire) and A/C compressor clutch ground circuit (Black wire). If test light comes on, go to next step. If test light does not come on, go to step 17).
Check for poor connections at A/C compressor clutch. Repair as necessary. Go to step 37). If no problem is found, go to step 33).
Check for an open or short to ground in A/C compressor clutch ignition feed circuit (Dark Green wire). Repair as necessary. After repairs, go to step 37). If no problem is found, go to step 34).
Leave PCM and A/C refrigerant pressure sensor disconnected at PCM. Turn ignition on. Using a voltmeter, measure voltage between A/C refrigerant pressure signal circuit (Red/Black wire) and ground. If reading is near zero volts, go to next step. If reading is not as specified, go to step 20).
Check for the following conditions:
- 5-volt reference "B" circuit (Gray wire) for a poor connection at PCM.
- 5-volt reference "B" circuit (Gray wire) for a poor connection at refrigerant pressure sensor.
- Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at PCM.
- Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at refrigerant pressure sensor.
- Sensor ground circuit (Black wire) for a poor connection at refrigerant pressure sensor.
  Repair as necessary and go to step 37). If no problem is found, go to step 36).
Locate and repair short to power in A/C refrigerant pressure signal circuit (Red/Black wire). Go to step 37).
Turn ignition on. Turn A/C off. Observe A/C REQUEST on scan tool. If A/C REQUEST displays YES, go to next step. If A/C REQUEST does not display YES, go to step 24).
Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on, A/C off. Using a voltmeter, measure voltage between ground and PCM harness connector C1, terminal No. 62 (A/C request circuit). If reading is near battery voltage, go to next step. If reading is not as specified, go to step 35).
Turn ignition off. Disconnect A/C control head/programmer. Turn ignition on. Check A/C request circuit for a short to power. Repair as necessary. Go to step 37). If no problem is found, diagnose A/C controls.
Disconnect A/C relay. Start engine and observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 29). If A/C compressor clutch is not engaged, go to next step.
Using a test light connected to ground, probe A/C compressor clutch ignition feed circuit (Dark Green wire) at A/C relay harness connector. If test light comes on, go to step 27). If test light does not come on, go to next step.
Replace A/C relay. Go to step 37).
Turn ignition off. Disconnect PCM harness connector C1. Using a test light connected to battery voltage, probe A/C relay driver circuit (Dark Green/White wire) at PCM connector. If test light comes on, go to next step. If test light does not come on, go to step 35).
Repair short to ground in A/C compressor clutch relay driver circuit (Dark Green/White wire). Go to step 37).
Turn ignition off. Disconnect A/C compressor clutch harness connector. Start engine and observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 33). If A/C compressor clutch is not engaged, go to next step.
Locate and repair short to power in A/C compressor clutch ignition feed circuit (Dark Green wire). Go to step 37).
Repair open or short to ground in ignition feed circuit (Pink wire) to A/C compressor relay. Go to step 37).
Replace A/C compressor relay. Go to step 37).
Repair A/C compressor clutch. Go to step 37).
Locate and repair open in A/C compressor clutch ground circuit (Black wire). Go to step 37).
Replace PCM. Go to step 37).
Replace A/C refrigerant pressure sensor. Go to step 37).
Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). With A/C off, start engine and let idle. Observe A/C compressor clutch. If A/C compressor clutch is engaged, go to step 21). If A/C compressor clutch is not engaged, go to next step.
Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on control head. Observe A/C compressor clutch. If A/C compressor clutch is engaged, system is okay. If A/C compressor clutch is not engaged, go to step 5).