Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis Diagnosis
The PCM will energize the A/C clutch whenever the engine is running less than 4700 RPM and A/C has been requested, unless any of the following conditions are met:
| • | A/C head pressure greater than 414 psi (2854 kPa) or less than 38 psi (262 kPa) (as determined by the A/C refrigerant pressure switches). |
| • | A/C evaporator temperature less than 2°C (36°F). |
| • | Engine at wide open throttle. |
| • | High power steering load. |
| • | Low ignition voltage. |
| • | Engine speed greater than 4700 RPM for 6 seconds. |
| • | ECT greater than 125°C (257°F). |
The A/C Compressor Clutch Control Circuit table should be used for diagnosing the electrical portion of the A/C circuit. SECTION 1 of the service manual should be used for diagnosing the refrigerant portion of the system.
A Scan Tool will be used in diagnosing the system, as it has the ability to read the A/C request input to the PCM, A/C compressor status, A/C system pressure, A/C evaporator temperature, as well as displaying when the PCM has commanded the A/C clutch ON.
Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis Compressor Control Circuit
Refer to
A/C Compressor Controls
for wiring view.
Circuit Description
This system consists of a HVAC control assembly, separate A/C refrigerant high and low pressure switches, separate A/C high and low temperature sensors, a control relay, the compressor clutch and the PCM.
When the HVAC control assembly is placed in the A/C mode, a request signal is sent to the PCM. The PCM will then energize the A/C clutch relay, unless abnormally high or low A/C pressure is detected by the A/C refrigerant pressure switches. The PCM also monitors the A/C low temperature sensors to cycle the A/C clutch ON and OFF. If the PCM detects an A/C evaporator temperature less than 2°C (36°F), the A/C clutch will be prohibited from being enabled. The PCM will also energize the cooling fans ON when A/C is requested. Refer to Electric Cooling Fans. The A/C compressor relay is controlled by the PCM so that the PCM can increase idle speed before turning ON the clutch or disable the clutch when high engine coolant temperature is detected or high engine RPM is detected.
Diagnostic Aids
| • | If DTC P1537 is stored as history, it is most likely that one of the A/C pressure switches opened. |
| • | If any PCM DTCs are set, perform those diagnostics before using this table. The A/C clutch is disabled for many DTCs. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
The outside air temperature must be great enough for the A/C compressor clutch to engage.
-
This step uses the Scan Tool to determine if there is an open or short.
-
This step checks the power feed circuit.
-
This step bypasses the relay.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain ON-BOARD DIAGNOSTIC (OBD) system check performed? | -- | Go to Powertrain OBD System Check | |||||||||
2 | Are any PCM DTCs stored? | -- | Go to DTCs that are set | |||||||||
Before continuing with diagnosis, the Outside Air Temperature (OAT) must be greater than the value specified.
Is the A/C compressor clutch engaged? | -23°C (-10°F) | |||||||||||
4 |
Is the compressor clutch engaged? | -- | Fault not present Refer to Diagnostic Aids | |||||||||
Does the Scan Tool display OK? | -- | |||||||||||
Does the test light illuminate on both terminals? | -- | |||||||||||
Is the A/C compressor clutch engaged? | -- | |||||||||||
8 |
Is the resistance less than the specified value? | 5 ohms | ||||||||||
9 | With the J 39200 multi meter, measure the resistance from a good Ground to terminal B of the A/C compressor clutch connector. Is the resistance less than the specified value? | 5 ohms | PCM / circuit(s) OK. Go to Air Conditioning Diagnosis in section 1 | |||||||||
10 |
Does the Scan Tool display ON? | -- | ||||||||||
11 |
Was a terminal contact problem found? | -- | ||||||||||
12 |
Is the voltage measured greater than the specified value? | 0.3 Volts | ||||||||||
13 |
Is the resistance less than the specified value? | 5 ohms | ||||||||||
14 | Does the test light illuminate on either terminal? | -- | ||||||||||
15 | Check terminal contact at the A/C relay. Was a terminal contact problem found? | -- | ||||||||||
16 | Check terminal contact at the A/C compressor clutch connector? Was a terminal contact problem found? | -- | ||||||||||
17 | Repair short to voltage on CKT 459. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
18 | Repair terminal contact. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
19 | Repair open in CKT 459. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
20 | Repair CKT 1039 between the splice and the terminal where the test light did not illuminate. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
21 | Check for the following and repair as necessary:
Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
22 | Replace the A/C relay. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
23 | Repair open in Ckt 59. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
24 | Replace the PCM. Refer to PCM Replacement/Programming Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
25 | Repair open in CKT 1350. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
