Scotsman B 1706 Manuel De Service page 19

Page 6
How it works
In the ice makers the water used to make the ice
is kept constantly in circulation by a water pump
which primes it to the spray system nozzles from
where it is diverted into the inverted cup molds of
the evaporator (Fig. A).
A small quantity of the sprayed water freezes into
ice; the rest of it cascades by gravity into the
sump assembly below for recirculation.
FREEZING CYCLE (Fig. B)
The hot gas refrigerant discharged out from the
compressor reaches the condenser where, being
cooled down, condenses into liquid. Flowing into
the liquid line it passes through the drier/filter,
then it goes all the way through the capillary tube
where it looses its pressure.
Next the refrigerant enters into the evaporator
serpentine (which has a larger diameter then the
capillary tube) and starts to boil off; this reaction
is emphasized by the heat transferred by the
sprayed water.
The refrigerant then increases in volume and
changes entirely into vapor.
The vapor refrigerant then passes through the
suction accumulator (used to prevent that any
small amount of liquid refrigerant may reach the
compressor) and through the suction line. In both
the accumulator and the suction line it exchanges
heat with the refrigerant flowing into the capillary
tube (warmer), before to be sucked in the
compressor and to be recirculated as hot
compressed refrigerant gas.
The freezing cycle on 1706, 2008, 2608, 2615,
3515 and 4422 is controlled by only the evaporator
thermostat which has its bulb in contact with the
evaporator serpentine while in 9522,7040,8040
and 9050 there is an second phase controlled by
an electronic timer.
The electrical components in operation during
the freezing cycle are:
COMPRESSOR
WATER PUMP
FAN MOTOR (in air cooled version)
On 1706 and 2008 air cooled versions (operating
with R134a) the refrigerant head pressure is
gradually reduced from the value of approx. 11
bar at beginning of the freezing cycle with the
machine at 21°C ambient temperature, to a
minimum value of approx. 7 bar just at the end of
the freezing cycle, few seconds before the starting
of the defrost cycle.
On 2608, 2615, 3515, and 4422 air cooled version
operating with R404A, the head pressure drops
from 19,5 bar to 13 bar while on the other bigger
models (5522, 7040, 8040 and 9050) the
refrigerant head pressure is kept between two
present values (17-13,5 bar) by means of a fan
pressure control.
PRINCIPLE OF OPERATION
The declining of the pressure is relied to the
reduction of the evaporating pressure, caused
by the progressive growth of the ice thickness
into the inverted cup molds and to the flow of air
drown through the air cooled condenser by the
fan motor. The above values are in relation as
well to the ambient temperature of the ice maker
site and they are subject to rise with the increase
of this temperature.
On 1706 and 2008 water cooled versions
(operating with R134a) the refrigerant head
pressure ranges between 8,5 and 10 bar being
controlled by an automatic hi pressure control
that energizes a water solenoid valve located on
the water line to the condenser, which rates the
cooling water to the condenser while on models
2608, 2615, 3515, 4422 and 5522 water cooled
version operating with R404A, the head pressure
ranges between 12 and 17 bar.
On 7040, 8040 and 9050 water cooled version
operating with R404A, the head pressure is
constant at 15 bar controlled by a water regulating
valve.
At starting of the freezing cycle the refrigerant
suction or lo-pressure lowers rapidly to 1,0 bar
(on 1706 and 2008) and to 2,5-3,0 bar on all other
models 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 bar on 1706
and 2008 and 1,4-1,5 bar in the other models
with the cubes fully formed in the cup molds.
DEFROST OR HARVEST CYCLE (Fig. D)
On 1706, 2008, 2608, 2615, 3515 and 4422 the
temperature of the evaporator thermostat, in
contact with the evaporator serpentine, drops to
a pre-set value it changes its electrical contacts
energizing the herebelow shown components.
(On 5522, 7040, 8040 and 9050 when the electro-
nic timer completes the second portion of the
freezing it changes its electrical contacts
energizing the same components).
COMPRESSOR
WATER INLET SOLENOID VALVE
HOT GAS SOLENOID VALVE
The incoming water, passing through the water
inlet valve and the flow control, runs over the
evaporator platen and then flows by gravity
through the dribbler holes down into the sump/
reservoir (Fig. C).
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, flows through the hot gas
valve directly into the evaporator serpentine by-
passing the condenser.