A/C Request Circuit Diagnosis

Diagnostic Chart:

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-A 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. Intermittent Conditions

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. Any A/C DTCs will disable the A/C system. Repair any A/C DTCs before proceeding.
3. The request circuit is shorted to voltage if the scan tool displays the A/C request as Yes.
5. 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.