Chart C-1B A/C Idle-Up Circuit Check

Diagnostic Chart:

A/C Idle-Up Circuit:

CIRCUIT DESCRIPTION
When the A/C compressor clutch is in operation, the A/C amplifier will send an A/C idle-up signal to the Engine Control Module (ECM). The ECM sends a signal to the Idle Speed Control (ISC) motor. This signal to the ISC motor will activate a plunger to open the throttle plate. As the throttle plate opens, the engine idle speed increases to prevent a rough idle or stalling condition.

CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Checks to see if the engine idle speed increases with A/C operation.
2. Checks for a faulty A/C amplifier. This also checks for an open or short to ground in BLU/RED wire.
3. Checks for an open, a short to ground or a short to voltage in the LT GRN/RED wire or for a faulty ECM.

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