Refer to
Heater- A/C Control and A/C Compressor Clutch Coil
.
Circuit Description
The C67 manual A/C system requests A/C operation via a wired A/C Request circuit between the HVAC control head and the powertrain control module (PCM).
The A/C clutch relay is PCM controlled. The PCM will engage the A/C clutch any time the A/C has been requested unless any of the following conditions exist:
| • | A high coolant temperature |
| • | A low A/C system pressure |
| • | A high A/C system pressure |
| • | A wide open throttle (WOT) |
| • | A high engine RPM |
| • | If 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 fans will be turned On when the A/C pressure reaches a predetermined pressure.
Diagnostic Aids
Before using this table, be sure no PCM DTCs are stored. The PCM may not activate the A/C clutch if certain DTCs are stored.
Use the J 35616 connector test adapter kit 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 the step numbers on the diagnostic table.
-
Any A/C DTCs will disable the A/C system. Repair any A/C DTCs before proceeding.
-
The request circuit is shorted to voltage if the scan tool displays the 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 Diagnostic Starting Point in HVAC 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 the applicable DTC tables | ||
Does the scan tool indicate the A/C Request is Yes? | -- | |||
4 | Turn the A/C On. Does the scan tool indicate the A/C Request is Yes? | -- | System OK | |
Is the voltage 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 a test lamp 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 Diagnostic Starting Point in HVAC for further diagnosis. Replace the HVAC control head. Is the action complete? | -- | -- | |
10 | Check for poor connections or terminal tension at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Was a problem found and corrected? | -- | ||
11 | Repair the open or high resistance in the A/C request circuit. Is the action complete? | -- | -- | |
12 | Repair the A/C request circuit shorted to ground. Is the action complete? | -- | -- | |
13 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |
14 |
Does the scan tool indicate the A/C Request is Yes with the A/C on and No with the A/C off? | -- | System OK |
