Refer to Engine Controls Schematics for wiring views.
Circuit Description
The A/C 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 sensor 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 not be 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 P 1537 is stored as history, it is most likely that one of the A/C pressure switches opened. Check for improper refrigerent pressures. |
| • | If any PCM DTCs are set, perform those diagnostics before using this table. The A/C clutch is disabled for many DTCs. |
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). |
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 | Did you perform the Powertrain On-Board Diagnostic (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 display indicate OK? | -- | |||||||||||
Does the test lamp illuminate on both terminals? | -- | |||||||||||
Is the A/C compressor clutch engaged? | -- | |||||||||||
8 |
Is the resistance less than the specified value? | 5 ohms | ||||||||||
9 | Using DMM J 39200 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 circuits OK. Go to Diagnostic System Check in HVAC Systems with A/C Automatic | |||||||||
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 lamp 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 the short to voltage on the A/C Control circuit. 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 the open in the A/C Control circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
20 | Repair the A/C Relay Power Feed circuit between the splice and the terminal where the test lamp 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 replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
23 | Repair the open in CKT 59. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
24 | Replace the PCM. Is the replacement 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 | -- |
