A heating, ventilation and air-conditioning (HVAC) a falling film evaporator in flow communication with a condenser. The falling film evaporator includes a separator to separate vapor from liquid refrigerant and a plurality of evaporator tubes through which a volume of thermal energy transfer medium is flowed. A distribution system is operably connected to the separator to distribute a flow of liquid refrigerant over the plurality of evaporator tubes. A primary feed conduit delivers a flow of refrigerant to the separator, and at least one secondary feed conduit is in flow communication with the primary feed conduit. At least one auxiliary valve is located at the secondary feed conduit to regulate flow into the separator from the primary feed conduit. At least one sensor senses a level of a refrigerant pool in the evaporator. The sensor is operably connected to the at least one auxiliary valve to control operation thereof.