Engine Control Module (ECM)
WARNING: This page is about a different car, the 1998 Honda Prelude. However, it is still accessible from the selected car via links, so may be relevant.
The ECM controls the coil circuit of the A/C compressor clutch relay. When the ECM senses ground through the A/C on input circuit, it grounds the coil circuit of the A/C compressor clutch relay.