A method of controlling a refrigeration system having a compressor, a condenser, an evaporator, and a variable speed condenser fan is provided. The method includes determining if a change in an ambient temperature or a compressor suction pressure is greater than a predetermined threshold, determining a near-optimal condensing pressure/temperature if the change in the ambient temperature or the compressor suction pressure is above the predetermined threshold, setting a condensing pressure setpoint based on the determined near-optimal condensing pressure/temperature, and setting a speed of the variable speed condenser fan based on the condensing pressure setpoint.