Engine Control Module (ECM)
WARNING: This page is about a different car, the 2001 Acura Integra, 2000 Acura Integra, and 1999 Acura Integra. However, it is still accessible from the selected car via links, so may be relevant.
The ECM monitors the A/C request circuit, which includes the A/C pressure switch, A/C thermostat, A/C switch, and blower switch (heater fan switch). If the ECM senses that the A/C request circuit is grounded, it energizes the A/C compressor clutch relay.