A/C Signal: Testing and Inspection

Diagnostic Chart - Part 1 Of 2:

Diagnostic Chart, Part 2 Of 2:

A/C Idle Circuit:

A/C IDLE CIRCUIT CHECK

Circuit Description:
The A/C solenoid vacuum (SV) valve is located in the center engine compartment mounted to the bulkhead. When the A/C switch is turned ON, the A/C amplifier sends the engine control module (ECM)/powertrain control module (PCM) an A/C ON signal. The ECM/PCM grounds the A/C SV valve, allowing additional air to enter the intake manifold. As a result of the increased air in he intake manifold, the engine idle speed is increased. The ECM/PCM sends the A/C amplifier an A/C cutout signal during certain heavy engine loads conditions. When the A/C amplifier receives this signal from the ECM/PCM, it immediately cuts out A/C compressor operation. When the engine returns to a lighter load, the ECM/PCM negates the A/C cutout signal. At this point, the A/C amplifier can resume normal cycling of the A/C compressor clutch.

Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Checks A/C ON output circuit.

2. Checks for an open or a short to ground in YEL/BLU or RED/WHT wire or a faulty A/C amplifier.

3. Checks for a short to ground in YEL/BLU or RED/WHT wire, a faulty A/C amplifier or a faulty ECM/PCM.

4. Checks for an open in the power feed to the A/C SV valve.

5. Checks for an open in WHT/RED wire or for faulty ECM/PCM.

6. Checks for a faulty A/C SV valve.

7. Checks A/C cutout circuit.

8. Checks for an open in RED/YEL wire.

9. Checks for an open or a short to ground in RED/YEL wire, a faulty A/C amplifier or a faulty ECM/PCM.

10. Checks for a faulty ECM/PCM or a faulty A/C amplifier.

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