Abstract: Constant condenser pressure is maintained in an air-cooled condenser of a refrigeration system which operates at either full capacity or reduced capacity depending on the heat load requirements. When operating at full capacity, the condenser head pressure will be held generally constant at a relatively high control point even in the presence of wide variations in condenser cooling air temperature. On the other hand, when the heat load requirements decrease and the refrigeration system switches to its reduced capacity operating mode, the control point automatically drops to a substantially lower level, whereupon the condenser pressure is maintained relatively fixed at that lower control point despite major changes in the condenser cooling air temperature. By automatically lowering the control point at reduced system capacity, maximum efficiency and economical operation are obtained.