Refer to
A/C Controls
.
Circuit Description
When A/C is selected through the A/C control head a 12 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 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 voltage below 10.5 volts. |
| • | Engine speed greater than 4500 RPM for 5 seconds or 5400 RPM. |
| • | ECT greater than 125°C (257°F). |
| • | IAT less than 5°C (41°F). |
Test Description:
The numbers below refer to 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 Important have been met.
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Checks for an A/C request signal from the control head to the PCM.
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Checks 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 | Was the Powertrain OBD System Check performed? | -- | ||||||||
Are any PCM DTCs stored? | -- | Go to applicable DTC | ||||||||
|
Important: : The following conditions must be met before continuing with this step:
Is the A/C Clutch engage? | -- | |||||||||
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 |
Was a problem found? | -- | Go to HVAC System Check in Heating, Ventilation and Air Conditioning | |||||||
8 |
Was a problem found? | -- | ||||||||
9 | Observe A/C refrigerant pressure display on the scan tool. Is indicated A/C pressure between the specified values? | 36 - 440 psi | ||||||||
10 |
Is high side refrigerant pressure within the specified values? | 36 - 440 psi | Go to Refrigerant Recovery and Recharging in Heating, Ventilation and Air Conditioning | |||||||
11 |
Does the scan tool display an A/C Highside pressure at the specified value? | 0 psi | ||||||||
Is the test light ON? | -- | |||||||||
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 |
Was a problem found? | -- | ||||||||
15 |
Is the test light ON? | -- | ||||||||
16 |
Was a problem found? | -- | ||||||||
17 |
Was a problem found? | -- | ||||||||
18 |
Does A/C Request display Yes? | -- | ||||||||
19 |
Does the voltage measure near the specified value? | B+ | ||||||||
20 |
Was a problem found? | -- | Go to HVAC System Check in Heating, Ventilation and Air Conditioning | |||||||
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. Is the action complete? | -- | -- | ||||||||
23 | Repair open or short to ground in ignition feed circuit to the A/C compressor relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
24 | Replace A/C compressor relay. Is the action complete? | -- | -- | |||||||
25 | Replace the A/C clutch plate and hub assembly or the A/C compressor clutch coil. Refer to Compressor Clutch Plate and Hub Assembly Removal or Air Conditioning Clutch Coil Removal in Heating. Ventilation and Cooling. Is the action complete? | -- | -- | |||||||
26 | Locate and repair open in A/C compressor clutch ground circuit. Is the action complete? | -- | -- | |||||||
27 |
Important: : The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | |||||||
28 | Replace A/C refrigerant pressure sensor. Is the action complete? | -- | -- | |||||||
29 |
Important: : The following conditions must be met before continuing with this step:
Is the A/C Clutch engage. | -- | System OK |
