The defrost termination/fan delay control is a temperature-activated, single pole-double throw switch controlled with a remote sensing bulb (Fig. 1). The control can be an adjustable type. One example of the installation of an adjustable defrost termination/fan delay control is on a walk-in freezer’s evaporator (Fig. 2).
The control is wired into the refrigeration circuit. The control’s remote sensing bulb is located high on the evaporator where the frost is likely to clear last. The function of this temperature-activated switch is to terminate defrost when the evaporator coil has been defrosted, and to delay the evaporator fans from coming on immediately after defrost.
Defrost time clocks can be programmed for certain defrost duration periods. This is a time duration set at the time clock in minute increments. For example, a defrost time clock on a freezer could be programmed to defrost every six hours (four times daily), and have defrost durations of 40 minutes. However, there will be times throughout the year where the coil does not need the entire 40 minutes. These times could be from low usage of the freezer where the door openings are minimal, or when the humidity is low and not much frost accumulates on the coil. This is where the defrost termination part of the control comes into play.
Read the full article to learn how the defrost termination & fan delay systems work