System Relay: Description and Operation

When the air conditioner switch is turned ON, while the engine is at idle, the Idle Speed Control (ISC) servo will be activated by the Control Unit to increase the idle speed, compensating for the extra load.
In order to keep the engine from stalling until the Idle Speed Control Servo has increased the idle, the Control Unit will open the A/C relay circuit momentarily.
Also, on vehicles equipped with automatic transmissions, the Control Unit will interrupt the A/C power relay circuit when the throttle valve is opened above 65°, to enhance acceleration performance