Defrosting - Zanussi Electrolux No Frost Refrigerator Service Manual

5.3 DEFROSTING

All the humidity in the compartment accumulates on the evaporator, which is the coldest part of the
compartment; periodically, every about 14 hours minimum with normal door openings (till 71 hours if the door is
never opened!), it is necessary to defrost the ice which forms on the battery, therefore, the electronic board
disconnect the circuit which powers the compressor (3) and the fan (24) and, after checking for the defrosting
heater, it powers the defrosting heater (9 e 9a) for about 20 minutes minimum. In case the defrosting heater is
interrupted or its connector is disconnected, the LED ON flashes and the defrosting heater lasts 1 hour.
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.
N.B.:
The defrosting activates with about half an hour delay if the door is opened between the 14th and 70th hour after
the last defrosting.
NOFROST REFRIGERATORS WITH ELECTRONIC TIMER 12/29