Scotsman B 21 WS Manuel De Service page 18

On 18-21-31-40 when the temperature of the
evaporator thermostat bulb reaches the value of
+3÷4°C their electrical contacts move back to the
previous position activating a new freezing cycle
and deenergizing both the hot gas and the water
inlet valves (closed).
On 50-65-90 as soon as the timer microswitch
completes the bottom part of the cam and it is
pushed again, it activates a new freezing cycle
deenergizing both the hot gas and the water inlet
valves (closed).
NOTE. On models 18, 21, 31 and 40 the
length of the defrost/harvest cycle (not
adjustable) changes according to the
ambient temperature (shorter for hi ambient
temperature and longer for low one).
COMPONENTS DESCRIPTION
A. WATER PUMP
The water pump operates continually throughout
the freezing cycle. The pump primes the water
from the sump to the spray system and through
the spray nozzles sprays it into the inverted cup
molds to be frozen into crystal clear ice cubes.
B. WATER INLET SOLENOID VALVE -
3/4 MALE FITTING
The water inlet solenoid valve is energized only
during the defrost cycle.
When energized it allows a metered amount of
incoming water to flow over the evaporator cavity
to assist the hot gas in defrosting the ice cubes.
The water running over the evaporator cavity
drops by gravity, through the dribbler holes of the
platen, into the sump reservoir.
On 18-21-31-40-50 water cooled versions the
water inlet solenoid valve has one inlet and two
outlets with two separate solenoids energized
the first (ice productioon) by the contacts 3-2 of
the evaporator thermostat and the second (water
cooled condenser) by a specific hi pressure
control.
C. HOT GAS SOLENOID VALVE
The hot gas solenoid valve consists basically in
two parts: the valve body and the valve coil.
During the defrost cycle the hot gas valve coil is
activated so to attract the hot gas valve piston in
order to give way to the hot gas discharged from
compressor to flow directly into the evaporator
serpentine to defrost the formed ice cubes.
D. BIN THERMOSTAT
The bin thermostat control body is located in the
front of control box behind the front panel.
The thermostat sensing tube is located into a
bulb holder on the side wall of the ice storage bin
where it automatically shuts the icemaker OFF
when in contact with the ice and re-starts the
icemaker when the ice is removed. Factory
settings are 1°C (35°F) OUT and 4°C (39°F) IN.
E. CUBE SIZE CONTROL (EVAPORATOR
THERMOSTAT)
18-21-31-40
The cube size control (evaporator thermostat)
body is located in the control box behind the front
panel; it's basically a reverse acting temperature
control which closes the contacts 3-2 when its
temperature decreases and closes the opposite
contacts 3-4 when the temperature rises.
The thermostat sensing bulb is located into a
plastic tube (bulb holder) secured by two clips
directly to the evaporator serpentine.
This control determines the length of the freezing
cycle and correspondingly the size of the cubes.
A lower setting will produce a larger cube
(oversize) while a higher setting a smaller cuber
(shallow size).
When closed on contacts 3-2 it activates the
defrost or harvest cycle components.
The cube size control is set up in the factory
(knob in the black dot position) and doesn't
require any adjustment when the ambient
temperature remains between 20 and 30°C
(70 and 90°F).
50-65-90
The evaporator thermostat with its sensing bulb
intimately in contact with the regrigerant outlet
tube from the evaporator senses the evaporating
refrigerant temperature (which declines in the
course of the freezing cycle) and when this one
reaches the pre-set value, it switches its contacts
from 3-4 to 3-2 to activate the finishing cycle (2nd
phase) which has a pre-set extension determined
by the large diameter lobe of the timer cam.
F. FAN MOTOR (Air cooled version)
The fan motor on 18-21-31-40 is electrically
connected in parallel to the water pump and it
operates continuously only during the freezing
cycle keeping the proper head pressure by
circulating air through the condenser fins.
On 50-65-95 the operation of fan motor is
controlled by a fan pressure control adjusted at
preset values.
G. COMPRESSOR
The hermetic compressor is the heart of the
refrigerant system and it is used to circulate and
retrieve the refrigerant throughout the entire
system. It compresses the low pressure
refrigerant vapor causing its temperature to rise
and become high pressure hot vapor (hot gas)
which is then released through the discharge
valve.
H. WATER SPRAY SYSTEM
Through its nozzles it sprays the water in each
individual cup to be frozen into ice.
I. SAFETY HI TEMPERATURE THERMOSTAT
Located in the control box it is a manual reset
switch that trips OFF the operation of the machine
when its bulb (located on the liquid line just
before the drier) reaches the temperature of
70°C (158°F).
Page 7