Component Diagnostic Charts/Tests

Chart C10C "A/C Cut-Out Relay":

Wiring Diagram "A/C Cut-Out Relay":

CHART C-10C

A/C CUT-OUT RELAY


Circuit Description:

The ECM controlled A/C cut-out relay is a normally closed relay. The ECM opens the relay by turning "ON" a quad-driver inside the ECM. This occurs during wide open throttle, overheated engine, and momentarily during engine start-up on a warm engine. Current flows through the closed relay when an A/C "ON" mode is selected, through the A/C clutch coil and to ground through a normally closed pressure cycling switch. The ECM also monitors the pressure cycling switch signal to control engine rpm during low refrigerant pressure at idle. The ECM also momentarily delays A/C clutch engagement during deceleration.


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

1. The A/C system must be fully charged so the pressure cycling switch contacts are closed.

2. If the ECM monitors a wide open throttle, simulated by fully depressing the TPS plunger, the A/C cut-out relay quad-driver in the ECM is turned "ON" allowing current to flow through the relay, opening the contacts and interrupting current flow to the A/C clutch. Any time the TPS is fully depressed, long term memory must be cleared to reset TPS range feature.


3. Grounding the ALDL test terminal should turn "ON" the A/C cut-out relay quad-driver in the ECM allowing current to flow through the test light.

4. This test will determine if the relay is at fault or ECM circuit operation is incorrect.

5. If the test light is "ON," the circuit is either grounded or ECM quad-driver is "ON." The ECM will have to be replaced if the test light goes "OFF" when ECM connector is disconnected, because the quad-driver inside the ECM is faulty.