Defrost heater
Also known as: defrost heating element, electric defrost heater
Short definitionA rod-shaped electric heater fitted in the evaporator fin block and the drip tray. It switches on during defrost to melt the frost, and is the most common defrost method in freezer rooms.
If the room is below 0 °C, or the evaporating temperature is lower than −5 °C, frost on the evaporator will not clear by itself. In electric defrost the compressor and fans stop, the stainless-sheathed heaters between the fins warm up, and the melt water runs from the tray to the drain. In a freezer room the drip tray gets a heater too; otherwise the water freezes again in the tray.
Heater power is roughly between half and all of the evaporator’s cooling capacity, and the control panel is sized for that load. A usual setting is 3–6 defrosts a day, 20–30 minutes at most; the fin sensor ends the defrost at between +8 and +15 °C. Most of the heat stays in the room, so unnecessary defrosts add load. An independent limit thermostat in the circuit guards against a welded contactor.