A/C Idle Circuit Diagnosis

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

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. The PCM sends a signal to the Idle Air Control (IAC) valve in order to increase the flow through the idle 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
Observe IAC Duty Cycle parameter on a scan tool while operating the A/C. The IAC Duty Cycle percentage should increase 4 to 12 percent when the A/C compressor is engaged. If the scan tool indicates that the IAC Duty Cycle is increasing when the A/C is turned On, but the idle quality is unsatisfactory, inspect the IAC system for proper operation.

Check for a faulty electrical connections at the A/C compressor control module and 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:
^ Any backed-out terminals
^ Any improper mating of terminals
^ Any broken electrical connector locks
^ Any improperly formed or damaged terminals
^ Any faulty terminal-to-wire connections
^ Any physical damage to the wiring harness
^ A broken wire inside the insulation
^ Any corrosion of the electrical connections, the splices, or the terminals

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 whether the PCM is receiving the A/C ON signal from the A/C compressor control module.
3. The A/C idle-up signal circuit at the PCM should indicate 0.0 volts with the A/C On.
4. The A/C idle-up signal circuit at the PCM should indicate B+ with the A/C Off.
7. The A/C cut-out signal circuit at the PCM should indicate 0.0 volts with the A/C Off.
8. The A/C cut-out signal circuit at the PCM should indicate B+ with the A/C On.