Compressor Controls

Chart C-10C - A/C Cut-Out Relay:

Wiring Diagram for Chart C-10C - A/C Cut-Out Relay:

CHART C-10C - A/C CUT-OUT RELAY

Circuit Description:


The ECM controlled A/C cut-out relay is designed to disengage the A/C compressor clutch during hard acceleration, if the engine should overheat and momentarily during engine start-up on a warm engine. The relay coil is supplied 12 volts from the A/C power feed circuit, and the ECM completes the ground through ECM terminal 19, energizing the normally open A/C Cut-Out Relay until A/C cut-out is required.

When a high TPS voltage (Wide Open Throttle) is sensed or an engine run signal is sensed with coolant temperature above a given amount, the ECM will cut-out the A/C clutch by switching the A/C cut-out relay to the open contact mode. There is also delayed engagement on start-up or cruise to decel., but only for about 3 seconds,

Test Description: Step numbers refer to step numbers on diagnostic chart.

1. Checks for normal A/C clutch operation at idle. If the clutch is not "ON," make certain the other A/C components are OK such as proper belt tension, sufficient Freon charge, A/C fuse not blown prior to checking relay.

2. Checks for normal A/C clutch cut-out during WOT. If the compressor disengages, for at least 10 sec., the system is OK. Clear long term memory.

3. By jumping across the relay coil connector terminals, it can be determined if the compressor remained engaged from a faulty relay (light "OFF") or from lack of signal to energize coil to open the relay points (light "ON").


4. By jumpering across relay contact point's connector terminals, it can be determined if lack of compressor operation is due to open relay contact points. If compressor engages, fault is in the relay or incorrect ECM circuit operation to disengage compressor clutch at wrong time.

5. Checks to see if "open" is in clutch coil (light "ON") or in clutch coil circuits (light "OFF"). If the test light is "OFF," there is either an open in 12 volt power feed to clutch coil or to ground from clutch coil.