The fan speed controllers are designed for speed variation of fan motors. Head pressure control of a refrigeration system, through speed variation of the fan on an air-cooled condenser, results in optimum performance throughout the year. Once the output drops below 30%, the fan is cut off.
A pressure-actuated control provides the most direct and fastest response to pressure variations in the refrigerant system. The controller varies the supply voltage to the motor from 30% to at least 95% over the proportional band using the phase-cutting principle.