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If the heater is in circuit (on) for 20 minutes in the defrost cycle, the following cycle is increased
by 2 hours; if it is connected for 30 minutes, it is maintained as is; if it is connected for 40 minutes,
it is decreased by 2 hours. Thus, the defrost cycles are set within the minimum range of 8 hours,
maximum range of 12 hours, increasing or decreasing by 2 hours, and no changes are made from 8
to 12 hours or 12 to 8 hours.
If the refrigerator is operating and is disconnected for a short time or if there is an electrical power
failure, the board's stored memory relating to the time that the resistance was connected during the
last defrost cycle is lost. Thus, when the shut-off temperature indicated by the potentiometer and the
refrigerator's sensor is reached, the compressor is turned off and a defrost cycle is carried out, in
order to record the time that the resistance is connected and to program the next defrost cycle.
DEFROST SENSOR
The sensor's function is to detect the amount of ice and time that the resistance is enabled; in order
to vary the time when the next defrost cycle should be enabled.
DEFROST THERMOSTAT
The defrost thermostat consists of a one-pole switch, a bimetallic disc and a pressure bolt. These
items are installed inside a metallic cylinder filled with epoxy putty. The cylinder has two
connection cables, which are welded to the internal terminals of the cylinder.
If the defrost sensor does not disable the resistance's operation after 35 minutes maximum and the
thermostat's disconnection temperature is reached, the bimetallic disc is bent, disconnecting all
terminals with the pressure bolt. When the evaporator's temperature drops enough (depending on
the thermostat's specifications), the bimetallic disc recovers its shape and connects the terminals
again. Thus, the bimetallic disc acts as a safety device to avoid the temperature reaching more than
22 °C (71.6 ºF).
BIMETALLIC SAFETY
THERMOSTAT
12
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