Browse quality defrost controls, time clocks, and general-purpose timers at F.W. Webb. A defrost timer is a motor-driven clock used in a refrigeration system to shut off the evaporator fan motors and compressor and regulate the amount of frost in the unit. Use a general-purpose timer for multiple applications that require keeping track of the minutes. Explore reliable defrost controls and time clocks from Paragon and Grasslin to find the right fit for your HVAC/R system.