A/C Idle Circuit Diagnosis

Wiring Diagram:

Circuit Description
This signal is sent from the A/C amplifier. The Powertrain Control Module (PCM) detects whether or not the A/C system is operating via the A/C amplifier. The extra load the A/C system demands from the engine requires a higher idle speed. When the PCM receives the A/C ON signal, it will activate the Idle Air Control (IAC) valve and the idle speed will increase.

Diagnostic Aids
An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation or a broken wire inside the insulation. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.

Use a scan tool in order to monitor the A/C switch parameter. When the A/C switch is in the ON position and the blower speed is in any speed except OFF, the scan tool should read ON. When the A/C switch is OFF, the scan tool should read OFF.

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
3. This step checks for the PCM signal voltage and for an open or a short to ground in the signal circuit, or for a malfunctioning PCM.
4. This step checks for a poor ground connection at the power steering pump and for a malfunctioning PSP switch.