COMBINED OIL RETURN AND COMPRESSOR DISCHARGE TEMPERATURE LIMITATION REGARDING FLOODED ECONOMIZER HEAT EXCHANGER

A refrigeration system of the type having an economizer cycle is provided with a null cycle, in addition to heating and cooling cycles, without shutting a compres- sor prime mover down, to preserve air flow in a conditioned space. First, second and third controllable valves respec- tively: (1) select main and auxiliary condensers, (2) open and close a liquid line, and (3) open and close a line which provides a warm liquid to an economizer heat exchang- er. The valves are controlled in at least one predeter- mined open/close pattern during a null cycle, and prefera- bly in a plurality of selectable predetermined open/close patterns, to provide a null cycle at any instant which sub- stantially matches the net heat gain or loss taking place in the conditioned space. Thus, the temperature of the served space will be more apt to remain in a null tempera- ture range close to set point, providing smoother and more accurate control over the temperature of the conditioned space for longer shelf life of perishables stored therein. The system achieves the latter by controlling cooling circulation in the compressor oil cooler.