This is an operation manual for ACU230. The device can be used to control two air conditioners, automatically switching from one air conditioner to the other at pre-determined times, or turning on both units when high indoor temperatures demand it. It also monitors the power sources for over-voltage, under-voltage, and over-current conditions, and provides dry contactors for each failure and AC ON/OFF status lights, making it possible to monitor it remotely. In addition, a fully illuminated front panel immediately reports to the operator the condition of the system. If the ACU230 control unit fails, it has two breakers for manual override, these breakers forces any of the AC ON/OFF. The user can remotely operate both AC from the control center away from station. The pc-board is protected with epoxy.