A condenser unit including a compressor for compressing a refrigerant vapor to provide a superheated refrigerant vapor exerting a head pressure, and a condenser for receiving the superheated refrigerant vapor and condensing the superheated refrigerant vapor therein, the condenser being located in an uncontrolled space with air therein at an ambient temperature. The condenser unit also includes a flow control means for controlling flow of the superheated refrigerant vapor from the compressor into the condenser, a rotatable condenser fan for moving air past the condenser to dissipate heat from the condenser, and a controller for controlling the flow control means and the speed of rotation of the condenser fan based on at least one preselected parameter, to maintain the head pressure within a predetermined range thereof.