A system and method that optimizes energy consumption in an HVAC unit by minimizing chiller activity. The system uses a control unit that overrides a thermostat in at least one room to close a cooling valve that leads a fluid input to the room. When multiple cooling valves are closed through the rooms, the consequential return fluid maintains greater cooling capacity and thus, the chiller does not have to operate at full capacity. The control unit individually controls components in the HVAC unit, which were previously controlled by switches on the thermostat. The control unit includes a temperature sensor that monitors an environment, such as the room and a plenum. The control unit also includes a control relay that closes the cooling valve on the HVAC unit when the predetermined temperature of the control unit is above the thermostat temperature set by a room occupant.