Air Conditioning (A/C) Request Circuit Diagnosis without CJ2
Circuit Description
The C67 A/C system (manual A/C), requests A/C operation via a wired A/C Request circuit between the HVAC control head and the PCM.
The A/C clutch relay is PCM controlled. The PCM will engage the A/C clutch any time A/C has been requested unless any of the following conditions exist:
| • | High coolant temperature. |
| • | Low A/C system pressure. |
| • | High A/C system pressure. |
| • | Wide open throttle. |
| • | High engine RPM. |
| • | Certain DTCs are set. |
When the heater and A/C control is placed in the A/C mode, a 12 volt signal is sent to the PCM from the HVAC control head. This is shown on the scan tool as A/C Request Yes. The PCM will then ground the A/C clutch relay control circuit to energize the A/C relay (if none of the above conditions exist).
When the relay is energized, the relay contacts close, and current flows through the relay to the A/C compressor clutch.
When A/C request has been detected by the PCM, the cooling fan(s) will be turned On when A/C pressure reaches a predetermined pressure.
Diagnostic Aids
Before using this table, be sure no PCM DTC(s) are stored. The PCM may not activate the A/C clutch if certain DTCs are stored.
Use the Connector Test Adapter Kit J 35616 for any test that requires probing the PCM harness connectors, electrical center fuse/relay cavities, component terminals or a component harness connector. Using this kit will prevent damage caused by improper probing of connector terminals.
If the problem is intermittent, refer to Intermittent Conditions for diagnosis.
Test Description
The numbers below refer to numbers on the diagnostic table.
-
A/C DTCs will disable the A/C system. Repair A/C DTCs before proceeding.
-
The request circuit is shorted to a voltage if the scan tool displays A/C request as Yes.
-
A problem exists with the request circuit between the PCM and the HVAC Programmer or the HVAC Programmer is malfunctioning if the test lamp did not illuminate. Refer to HVAC Blower Controls System Check for further diagnosis.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Are any A/C DTCs set? | -- | Go to applicable DTC table. | ||
Does the scan tool indicate A/C Request Yes? | -- | |||
4 | Turn the A/C On. Does the scan tool indicate A/C Request Yes? | -- | System OK | |
5 |
Does the DMM display near the specified value when the A/C is enabled? | B+ | ||
6 |
Does the DMM indicate continuity? | -- | ||
7 | Probe the A/C request circuit at the PCM harness connector using test lamp J 35616-200 connected to B+. Does the test lamp illuminate? | -- | ||
8 | Check the A/C request circuit for a short to voltage and repair as necessary. Was a problem found and corrected? | -- | ||
9 |
Important: Before replacing the HVAC control head, refer to HVAC Blower Controls System Check for further diagnosis. Replace the HVAC control head. Is the action complete? | -- | -- | |
10 | Check for poor connections/terminal tension at the PCM. Refer to Intermittents and Poor Connections Diagnosis . Was a problem found and corrected? | -- | ||
11 | Repair the open/high resistance A/C request circuit. Is the action complete? | -- | -- | |
12 | Repair the A/C request circuit shorted to ground. Is the action complete? | -- | -- | |
13 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming Is the action complete? | -- | -- | |
14 |
Does the scan tool indicate A/C Request Yes with the A/C on and No with the A/C off? | -- | System OK |
Air Conditioning (A/C) Request Circuit Diagnosis with CJ2
Circuit Description
The CJ2 A/C system (automatic A/C), requests A/C operation via a Class 2 serial data message sent from the HVAC control head to the PCM.
The A/C clutch relay is PCM controlled. The PCM will engage the A/C clutch any time A/C has been requested unless any of the following conditions exist:
| • | High coolant temperature. |
| • | Low A/C system pressure. |
| • | High A/C system pressure. |
| • | Wide open throttle. |
| • | High engine RPM. |
| • | Certain DTCs are set. |
When the heater and A/C control is placed in the A/C mode, a Class 2 Serial Data message is sent to the PCM requesting A/C operation. This is shown on the scan tool as A/C Request Yes. The PCM will then ground the A/C clutch relay control circuit to energize the A/C relay (if none of the above conditions exist).
When the relay is energized, the relay contacts close, and current flows through the relay to the A/C compressor clutch.
When A/C request has been detected by the PCM, the cooling fan(s) will be turned On when A/C pressure reaches a predetermined pressure.
Important: The wired A/C Request circuit may be present at the PCM connector. This wire is not used with the CJ2 HVAC system and there is no failure mode of this circuit that affects system operation.
Diagnostic Aids
Before using this table, be sure no PCM DTC(s) are stored. The PCM may not activate the A/C clutch if certain DTCs are stored.
If the problem is intermittent, refer to Intermittent Conditions for diagnosis.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- |
