A/C Idle Circuit Diagnosis

Circuit Description
The A/C compressor control module sends an A/C idle-up signal to the powertrain control module (PCM) when the A/C compressor clutch is ON (engaged). The PCM sends a signal to the idle air control (IAC) valve in order to increase the flow through the idle (bypass) air passage. The engine idle speed increases as more air flows through the idle air passage. The increase in the idle speed prevents a rough idle or stalling condition.

Diagnostic Aids
Check for a faulty electrical connection to the PCM. An intermittent malfunction may be caused by a fault in the A/C idle-up electrical circuit. Inspect the wiring harness and components for any of the following conditions:
^ Backed out terminals.
^ Improper mating of terminals.
^ Broken electrical connector locks.
^ Improperly formed or damaged terminals.
^ Faulty terminal to wire connections.
^ Physical damage to the wiring harness.
^ A broken wire inside the insulation.
^ Corrosion of electrical connections, splices, or terminals.
If no problem was found in the A/C idle-up circuit check, refer to Symptoms. Testing and Inspection

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step checks for an increase in the idle speed with the A/C ON.
3. The A/C idle-up signal circuit at the PCM should indicate 0.0 volts with the A/C ON (operating).
4. The A/C idle-up signal circuit at the PCM should indicate B+ with the A/C OFF (not operating).
7. The A/C cut-out signal circuit at the PCM should indicate 0.0 volts with the A/C OFF (not operating).
8. The A/C cut-out signal circuit at the PCM should indicate B+ with the A/C ON (operating).