Follett 01310564

PROBE CONTROL/DEFROST NTC

Controls of all kinds are integral parts of restaurant equipment operation. A control is a switch or other device by which a machine is regulated. A control may be manual or automatically operated. An electro-mechanical control typically consists of multiple relays, timers, and/or counters wired together on an enclosure panel. Electro-mechanical control is also referred to simply as "Relay Control", which is a more accurate term since solid state electronic relays, timers, and counters are standard components. Contactors, motor and compressor starters, valves, thermostats, and other output devices are used to turn on/off motors, indicator lights, heating elements, and other components used in the equipment.

The defrost mechanism in a refrigerator heats the cooling element (evaporator coil) for a short period of time and melts the frost that has formed on it. The resulting water drains through a duct at the back of the unit. Defrosting is controlled by an electric or electronic timer: For every 6, 8, 10, 12 or 24 hours of compressor operation it turns on a defrost heater for 15 minutes to half an hour.

A defrost thermostat opens the heater circuit when the evaporator temperature rises above a preset temperature, 40°F (5°C) or more, thereby preventing excessive heating of the freezer compartment. The defrost timer is such that either the compressor or the defrost heater is on, but not both at the same time.