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With the unit installed in a normal location (21°C
ambient temperature) at the start of the freezing
cycle the refrigerant suction or lo-pressure lowers
rapidly to 1.0÷0.9 bars (14÷12 psig) then it
declines gradually - in relation with the growing of
the ice thickness - to reach, at the end of the
cycle, approx. 0÷0.1 bars (0÷1.5 psig) with the
cubes fully formed in the cup molds.
The total length of the freezing cycle ranges from
20 to 22 minutes.
DEFROST OR HARVEST CYCLE
As the electronic timer has carried the system
throughout the third phase of freezing cycle or as
soon as the second phase T2 is over (when its
length has been as long as 35 to 45 minutes) the
defrost cycle starts.
NOTE. The length of the defrost cycle (not
adjustable) is related to the length of the
second phase of freezing cycle T2 as detailed
in Table B.
The electrical components in operation during
this phase are:
COMPRESSOR
WATER INLET SOLENOID VALVE
HOT GAS SOLENOID VALVE
WATER DRAIN SOLENOID VALVE
WATER PUMP and FAN MOTOR for the first
15-20 seconds
The incoming water, passing through the water
inlet valve and its flow control (Fig. C) runs over
the evaporator platen and then flows by gravity
through the dribbler holes down into the sump/
reservoir.
The water filling the sump/reservoir forces part of
the surplus water from the previous freezing
cycle to go out to the waste through the overflow
pipe. This overflow limits the level of the sump
water which will be used to produce the next
batch of ice cubes.
Meanwhile, the refrigerant as hot gas, discharged
from the compressor (Fig. D) flows through the
hot gas valve directly into the evaporator
serpentine by-passing the condenser.
The hot gas circulating into the serpentine of the
evaporator warms up the copper molds causing
the defrost of the ice cubes. The ice cubes,
released from the cups, drop by gravity onto a
slanted cube chute, then through a curtained
opening they fall into the storage bin.
On the versions equipped with the water drain
valve, the water pump remains in operation,
during the first 15-20 seconds of the defrost
cycle, to pump out, trough the opened water
drain valve, the remaining water (reach of minerals
and deposits) of the previous freezing cycle.
NOTE. The length of the defrost cycle (not
adjustable) changes in accordance with the
duration of the second portion of the freezing
cycle T2 and is related as well to the ambient
temperature (as shown on Table B). Infact in
high ambient temperature situation the defrost
cycle is abbreviated so to recover some of
the time used for the longer freezing cycle.
At the end of the defrost cycle, both the hot gas
and the water inlet valves close and the machine
starts again a new freezing cycle.
OPERATION - CONTROL SEQUENCE
At the start of freezing cycle the evaporator
temperature sensor controls the length of the
first T1 and second T2 portion of the freezing
cycle. As it senses the predetermined evaporating
temperature of -13°C (8.5°F) it supplies a low
voltage current to the P.C. BOARD in order to
activate the electronic timer which takes over
the control of the remaining portion of the freezing
cycle for a pre-fixed time Ta subordinated to the
DIP SWITCH keys setting (see Tab. C).
NOTE. The evaporator temperature
sensor,factory pre-set, is the same for all the
models and is not adjustable in the field.
During the normal operation mode the length or
the total time of the freezing cycle ie equal to the
sum of the three partial times i.e.:
Tc = T1 + T2 + Ta
In case the length of the second portion of the
freezing cycle or time T2 gets long as to be
between 35 and 45 minutes, the total length of
the freezing cycle will be limited to:
Tc = T1 + T2
skipping the added time Ta, controlled by the
electronic timer.
If instead the time T2 gets longer than 45 minutes
the unit stops immediately with the lighting up of
the warning 2nd RED LIGHT.
The same could happen in case the time T1
(1st portion of freezing cycle) gets longer than
15 minutes.
Once completed the freezing cycle 2nd or 3rd
phase (this last one is dependent of the length of
the second phase of freezing cycle - T2) the
system goes automatically into the defrost cycle
Ts.
The defrost cycle also has a pre-fixed length that
can vary in relation to the time T2, as shown in
Table B.
At completion of the defrost cycle the P.C. BOARD
put the unit into a new freezing cycle.
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