Circuit/System Description
WARNING: This page is about a different car, the 2017 Chevrolet Spark. However, it is still accessible from the selected car via links, so may be relevant.
When the A/C switch is pressed, the HVAC control module sends an A/C request signal to the body control module (BCM). The BCM sends an A/C request message to the engine control module (ECM) via CAN-Bus and supplies voltage to the A/C LED signal circuit.