A/C Signal: Description and Operation

These input signals indicate to the ECU that air conditioning switch is in the ON position, and that a signal needs to be sent to engage the compressor clutch. Before the A/C clutch can be engaged, the ECU will increase the engine speed, via the Idle Speed Actuator (ISA) Motor, to ensure that the added load of the A/C compressor will not kill the engine.

The ECU increases the idle through both the A/C select and A/C request controls. This circuit is shared by the power steering pressure switch, and both provide input to the ECU that will cause the idle speed to be increased.