Refer to
HVAC Control
.
When an A/C mode is selected, the A/C control head or the A/C programmer supplies a 12 volt signal to the PCM A/C request input. The A/C compressor clutch relay is controlled by the PCM. The PCM provides a ground path for the A/C relay coil. When the A/C compressor relay is engaged battery voltage is supplied to the compressor clutch coil. The PCM will enable the A/C compressor clutch whenever the engine is running and the A/C has been requested unless one or more of the following conditions are present:
• | Throttle angle is greater than 90 percent. |
• | A/C head pressure is greater than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor). |
• | Ignition 1 voltage is below 10.5 volts. |
• | Engine speed is greater than 4,500 RPM for longer than 5 seconds. |
• | Engine speed is greater then 5,400 RPM for any amount of time. |
• | ECT is greater than 125°C (257°F). |
• | IAT is less than 5°C (41°F). |
Any of the conditions described above will inhibit A/C compressor relay operation.
Check for the following conditions:
• | Poor connection at the PCM, A/C compressor, A/C control head, A/C relay, or A/C refrigerant pressure sensor. |
Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
• | Damaged harness. |
Inspect the wiring harness for damage. |
• | If the harness appears to be OK, disconnect the PCM, turn the ignition ON and observe a voltmeter connected to the A/C relay control circuit at the PCM harness connector while moving connectors and wiring harnesses related to the A/C relay. A change in voltage will indicate the location of the malfunction. |
Check for conditions that will disable A/C operation:
• | Throttle angle greater than 90%. |
• | A/C head pressure greater than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor). |
• | Ignition 1 voltage less than 10.5 volts. |
• | Engine speed greater than 4500 RPM for longer than 5 seconds. |
• | Engine speed greater than 5400 RPM for any amount of time. |
• | ECT greater than 125°C (257°F). |
• | IAT less than 5°C (41°F). |
Number(s) below refer to Step number(s) on the diagnostic table:
Stored diagnostic trouble codes may disable the A/C compressor. This diagnostic table may lead to improper diagnosis and replacement of good parts if diagnostic trouble codes are present.
The A/C compressor clutch should not be engaged with the engine running if an A/C mode is not selected at the control head.
The A/C compressor clutch should engage if the appropriate conditions have been met.
Checks for an A/C request signal from the control head to the PCM.
Checks the ignition feed circuit to the A/C relay.
Determines whether the condition is caused by a malfunctioning A/C relay or circuitry.
Determines if the PCM is turning the A/C relay ON due to a false A/C request.
Isolates the problem to the A/C control head or the PCM.
Determines if the A/C relay is malfunctioning or the A/C relay control circuit is grounded all the time.
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||||
Are any PCM DTC(s) stored? | -- | Diagnose DTC(s) first. Go to Powertrain Control Module Diagnosis | ||||||||||||
Important: Before continuing with diagnosis, the following conditions must be met:
Is the A/C compressor clutch engaged? | -- | |||||||||||||
Is the A/C compressor clutch engaged? | -- | Go to Diagnostic Aids | ||||||||||||
5 | With an A/C mode still selected, observe A/C Request on the scan tool. Does A/C Request display Yes? | -- | ||||||||||||
Does the voltage measure near the specified value? | B+ | |||||||||||||
7 |
Was a problem found? | -- | Go to A/C Controls diagnostics in Heater, Ventilation, And Air Conditioning | |||||||||||
8 |
Was a problem found? | -- | ||||||||||||
9 | Observe A/C High Side Pressure on the scan tool. Is indicated A/C High Side Pressure between the specified values? | 0.35-4.27V | ||||||||||||
10 |
Is high side refrigerant pressure within the specified values? | 234-2854 kPa (34-414 psi) | Go to Refrigerant Recovery and Recycling, Adding Oil, Evacuating and Recharging Procedures in Heater, Ventilation and Air Conditioning | |||||||||||
11 |
Is any resistance higher than the specified value? | 5 ohms | ||||||||||||
Is the test light ON? | -- | |||||||||||||
Connect a fused jumper between the ignition feed circuit and A/C compressor clutch control circuit (CKT 59) at the A/C relay connector. Does the A/C compressor clutch engage? | -- | |||||||||||||
14 |
Was a problem found? | -- | ||||||||||||
15 |
Is the test light ON? | -- | ||||||||||||
16 |
Was a problem found? | -- | ||||||||||||
17 |
Was a problem found? | -- | ||||||||||||
18 |
Does the voltage measure near the specified value? | -- | ||||||||||||
19 |
Was a problem found? | -- | ||||||||||||
20 | Locate and repair short to voltage in the A/C refrigerant pressure signal circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
Does A/C Request display Yes? | -- | |||||||||||||
Does the voltage measure near the specified value? | B+ | |||||||||||||
23 |
Was a problem found? | -- | Go to A/C Controls Diagnosis in Heater, Ventilation, and Air Conditioning | |||||||||||
24 |
Is the A/C compressor clutch engaged? | -- | ||||||||||||
25 | Probe the A/C compressor clutch control circuit (CKT 59) at the A/C relay harness connector with a test light to ground. Is the test light ON? | -- | ||||||||||||
26 | Replace the A/C relay. Is action complete? | -- | -- | |||||||||||
Is the test light ON? | -- | |||||||||||||
28 | Repair short to ground in the A/C compressor clutch relay control circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
29 |
Is the A/C compressor clutch engaged? | -- | ||||||||||||
30 | Locate and repair short to voltage in the A/C compressor clutch control circuit (CKT 59). Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
31 | Repair open or short to ground in ignition feed circuit to the A/C compressor relay. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
32 | Replace the A/C compressor relay. Is action complete? | -- | -- | |||||||||||
33 | Repair the A/C compressor clutch. Refer to V5 Air Conditioning Compressor Service. Is action complete? | -- | -- | |||||||||||
34 | Locate and repair open in the A/C compressor clutch ground circuit (CKT 450). Is action complete? | -- | -- | |||||||||||
Replace the PCM. Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||||||||||||
36 | Replace the A/C refrigerant pressure sensor. Refer to On-Vehicle Service in Heater, Ventilation and Air Conditioning. Is action complete? | -- | -- | |||||||||||
37 |
Important: Before continuing with diagnosis, the following conditions must be met:
Is the A/C compressor clutch engaged? | -- | ||||||||||||
38 |
Is the A/C compressor clutch engaged? | -- | System OK |