Operation Of The Defrost System - Electrolux DF36 Service Manual

1.4 Operation of the defrost system

To check the operation of the product defrost system the steps bellow should be followed:
1.4.1 Forced Defrost
With the help of a screwdriver, turn the timer mechanism in the clockwise sense until you hear the first click, so
as to manually advance it to the defrost position. At this point, a change occurs in the timer contacts going from
1-4 to 1-2, turning off the product compressor.
1.4.2 Verify if there was change of the timer contacts which provide energy for the resistances.
Now, there should be alternate tension (127 or 220V) between the contacts 1-2 of the timer.
The freezer temperature being bellow -6 ± 4
which are connected in parallel.
At this point, the timer motor stops, because being serially connected to the resistances it has an elevated
impedance (approximately 16.000) in relation to the parallel value between the resistances. The current that flows
through the circuit tend to follow the path with lesser resistance.
The defrost operation is monitored by the bimetallic defrost thermostat. When the temperature achieves +25 ± 3
º
C in the thermostat, its contact opens interrupting the current being passed to the resistances. At this point, the
timer motor is energized again, resuming operation and turning the timer mechanism for 10 minutes. During this
period of time, the product is still with contacts 1-2 on and the motofan, resistances and the compressor are turned off.
We call this 10 minutes period of dripping time. After this period of time, there is a change in the timer contacts
to 1-4, activating the compressor if the refrigerator thermostat is requiring its activation.
1.4.3 Checking the resistances with forced defrost
! Defrost Resistance ! ! !
!
Disconnecting the freezer evaporator defrost resistance male connector, using the resistance scale of the multimeter,
it is possible to verify its resistance value in ohms (see the table bellow for comparison values).
In the resistance female connector located in the cabinet, it is possible to measure the alternate tension127V
or 220V), if the defrost is activated, according to the procedure described above. If there is tension in this
connector, that means that the thermal fuse and the defrost thermostat are allowing the defrost operation.
térmico e o termostato de degelo estão permitindo a operação de degelo.
OHMIC RESISTANCE OF THE
DEFROST RESISTANCE AT +23ºC
RESISTANCE MEASUREMENT
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º
C, there will be current feeding the defrost and gutter resistances,
FOR 127V
57,9 to 70,39
BRIDGE BETWEEN
*
THE CONNECTORS
POWER VOLTAGE
MEASUREMENT WITH
DEFORST IN OPERATION
5
FOR 220V
180,8 to 210,9
* Attention: The bridge (pink
wire) between the evaporator
resistance and the bimetal-fuse
connectors should present
continuity between them,
otherwise there won't be
current to feed the defrost
resistance.