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1.2.4 DEFROSTING PHASE
When the refrigerator is in operation, every time the door is opened to take some product,
humidity contained in the atmospheric air deposits on the evaporator, jeopardizing its
efficiency. To solve this problem, an automatic system is provided, which defrosts the
evaporator (20) by supplying heat and drains the resulting water into the plastic tray (85)
positioned in the compressor seat, where it is evaporated. The activation of the defrosting
system, happening periodically every 6 hours, is controlled by a timer (TS) (81) and takes a
predefined time of 22.5 minutes max.: during the standby period of 22.5 minutes the heat is
supplied to the evaporator by means of an electrical heater (evaporator heater) (REV) (66),
and is controlled by the end-of-defrosting thermostat (KFS) (5), positioned on the evaporator
(20), reducing it to the minimum possible; in the meantime the internal motor fan (MI) (39),
stops, and the cut-off valve (VM) (84), governing the refrigerant flow to the evaporator, locks
the refrigerant inside the condenser, while the compressor (CO) (12) and the condenser
motorfan (MC) (38) continue to run, reducing the evaporator pressure till the low pressure
pressostat (PBP) (88) stops them.
To avoid ice forming on the evaporator draining tube (7), an electrical heater (gutter heater)
(RSG) (65) provides to maintains it warm, so that the resulting water can flows away from the
inner tank directly into the water tray (85), where a stainless steel pipe (58), connected to the
compressor outlet pipe, helps it to evaporate.
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1.2.5 OTHER FUNCTIONS
To avoid an excessive loss of cold during the door opening, a proximity door switch (IP)
(36) has been inserted to stop the internal motor fan (MI) (39): every time the door is opened,
the inside ventilator stops, reducing the hot air input inside the machine.
An always active wire-wound resistor (RT) (64), located inside the door frame, prevents
the door frame itself from condensation.
The door external flat glass surface is electrically heated (RV) to avoid glass condensation
and accelerate glass defogging every time the door is opened.
Both these door heaters are electrically supplied by an isolation transformer (TI) (82).
A green lighting main switch (IG) (31) disconnects the freezer from voltage supply by
means of a main relay (RG) (63).
By means of the lamps switch (IL) (32) the inner lamps and the display lamp can be
switched on and off; this lamps switch has also the function to light when the defrosting
phase is active, to inform the user about the state of the freezer.
An EMC (Electro-Magnetic Compatibility) filter (FRF) (22) avoids any electrical noise
emission on the voltage supply net.
wired in parallel on the compressor; thus the internal temperature rises, and when it
reaches the value correspondent to the thermostat differential, the thermostat itself acts
again on the cut off valve solenoid coil, opening the valve: the refrigerant can flow to the
evaporator making its pressure rising, till the low pressure pressostat turns again the
compressor and the condenser motor fan on. This function is called "pump down" cycle.The
length of the standby period depends on the ambient temperature and on the quantity of
product preserved inside the machine.
The tank thermostat (TC) (80) has 7 adjustment positions, from 1 to 7: the higher the
number is, the colder the tank temperature is.
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