Circuit Description
WARNING: This page is about a different car, the 2005 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.
The A/C amplifier outputs the magnetic clutch ON signal from AC1 terminal to the ECM. When the ECM receives this signal, it sends a signal from ACT terminal and the A/C amplifier switches the A/C magnetic clutch relay ON. This turns the A/C magnetic clutch on.