Compressor Circuit: Description
WARNING: This page is about a different car, the 2007 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
The A/C amplifier outputs the magnet clutch ON signal to the ECM by way of MPX line. The ECM receives this signal, and it sends a signal from terminal ACMG to the magnet clutch relay, turning the magnet clutch ON.