NOFROST UNDERCOUNTER FREEZERS WITH ELECTRONIC TIMER
11/20
5.4 DEFROSTING
All the humidity in the compartment accumulates on the evaporator, which is the coldest part of the
compartment; periodically, every about 19 hours minimum, it is necessary to defrost the ice which forms on the
battery itself, therefore the electronic control, after checking for the defrosting heater (see paragraph 6.3),
disconnect the circuit which powers the compressor
(3)
and the
(24)
and powers the circuit of the defrosting
heater
(9)
for a time of about 20 minutes.
The heat generated by the defrosting heater does not affect the temperature of the freezer compartment or the
temperature of the food packages, since the whole thermal energy is consumed in the defrosting process of the
ice on the evaporator.
After 20 minutes, the board detects every minute the signal of the defrosting process in order to determine the
intervention of the defrosting cut-out switch
(27)
.
When the defrosting cut-out switch intervenes, the electronic control switches on the compressor again
(3)
with a
5 minute delay.
After another 3 minute delay, when the air is already cold, the fan also switches on again
(24)
.
If for any reason, the defrosting cut-out switch does not intervene
(27)
and the temperature of the battery rises
up to +40 °C, the defrosting heater
(9)
will be switched off by the safety thermal switch
(26)
.
Moreover, if 1 hour after the defrosting start the safety thermal switches did not switch off, the electronic board
switches off anyway the defrosting heater and the process carries on.
The arrows in the picture indicate the current path.