Refer to Engine Controls Schematics
Heater A/C Controls
.
Circuit Description
When A/C is selected through the A/C controller a 12.0 volt signal is supplied to the A/C request input of the PCM. The A/C compressor clutch relay is controlled through the PCM. The PCM monitors the A/C refrigerant pressure. If the A/C refrigerant pressure, and engine operating conditions are within a specific calibrated acceptable ranges the PCM will enable the A/C compressor relay. This is accomplished by providing a ground path for the A/C relay coil within the PCM. When the A/C compressor relay is enabled 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 any of the following conditions are met:
| • | Throttle greater than 96 percent. |
| • | A/C head pressure greater than 440 psi (4.27 volts) or less than 36 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor). |
| • | Ignition voltage below 10.0 volts. |
| • | Engine speed greater than 4700 RPM for 5 seconds or 5400 RPM. |
| • | ECT greater than 145°C (255°F). |
| • | IAT less than 5°C (41°F) |
Diagnostic Aids
Inspect for the following conditions:
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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.
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Stored Diagnostic Trouble Codes (That may not illuminate the Malfunction indicator Lamp) 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.
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The A/C compressor clutch should apply if the conditions under the Notice have been met.
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Inspects for an A/C request signal from the control head to the PCM.
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Inspects the ignition feed circuit to the A/C relay.
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Determines whether the A/C relay or the circuitry is at fault.
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Determines whether or not the PCM is turning the A/C relay on due to a false A/C request.
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Isolates problem to the A/C control head or the PCM.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
Are any PCM DTCs stored? | -- | Go to the applicable DTC table | ||||||||
|
Important: : The following conditions must be met before continuing with this step:
Is the A/C clutch engaged? | -- | |||||||||
4 |
Is the A/C compressor clutch engaged? | -- | Go to Diagnostic Aids | |||||||
5 | With Defrost or Max mode selected, monitor A/C Request display on the scan tool engine data list. Does A/C Request display Yes? | -- | ||||||||
Does the voltage measure near the specified value? | B+ | |||||||||
7 |
Did you find and correct the condition? | -- | Go to Diagnostic System Check | |||||||
8 | Inspect the A/C request circuit for a faulty connection at the PCM. Refer to Testing for Continuity , Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals , and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
9 | Observe A/C refrigerant pressure display on the scan tool. Is A/C pressure indicated between the specified values? | 36 - 440 psi | ||||||||
10 |
Is high side refrigerant pressure within the specified values? | 36 - 440 psi | Go to Diagnostic System Check | |||||||
11 |
Does the scan tool display an A/C Highside pressure at the specified value? | 0 psi | ||||||||
Did the test lamp illuminate? | -- | |||||||||
Connect a fused jumper between the ignition feed circuit and A/C compressor clutch control circuit at the A/C relay connector. Does the A/C compressor clutch engage? | -- | |||||||||
14 | Inspect for faulty connections at A/C relay. Refer to Testing for Continuity , Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals , and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
15 |
Did the test lamp illuminate? | -- | ||||||||
16 | Inspect for faulty connections at the A/C compressor clutch. Refer to Testing for Continuity , Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals , and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
17 | Inspect for an open or short to ground in the A/C compressor clutch control circuit. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
18 |
Does A/C Request display Yes? | -- | ||||||||
19 |
Does the voltage measure near the specified value? | B+ | ||||||||
20 |
Did you find and correct the condition? | -- | Go to Diagnostic System Check | |||||||
Is the A/C compressor clutch engaged? | -- | |||||||||
Locate and repair short to voltage in the A/C compressor clutch control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | ||||||||
23 | Repair open or short to ground in ignition feed circuit to the A/C compressor relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |||||||
24 | Replace the A/C compressor relay. Did you complete the replacement? | -- | -- | |||||||
25 | Repair A/C compressor clutch. Refer to Air Conditioning Clutch Coil Removal in HVAC. Did you complete the repair? | -- | -- | |||||||
26 | Locate and repair open in A/C compressor clutch ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |||||||
27 |
Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | |||||||
28 | Replace A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement . Did you complete the replacement? | -- | -- | |||||||
29 |
Important: : The following conditions must be met before continuing with this step:
Is the A/C Clutch engaged? | -- | System OK |
