Freezing Cycle; Principle Of Operation; How It Works - Scotsman ACM 85 Service Manual

Page 18
In the SCOTSMAN cube ice makers the water
used to make the ice is kept constantly in
circulation by an electric water pump which primes
it to the spray system nozzles from where it is
diverted into the inverted mold cups of the
evaporator. 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

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, due to the heat exchanging action, it
looses some of its heat content so that its pressure
and temperature are lowered as well.
Next the refrigerant enters into the evaporator
serpentine (which has a larger I.D. then the
capillary) 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 is controlled by the evaporator
temperature sensor (which has its probe in contact
with the evaporator serpentine) that determines
the length of its first portion of the cycle.
When the temperature of the evaporator
serpentine drops to a pre-set value, the evaporator
sensor probe changes its electrical resistance
allowing a low voltage current (15 volts) to flow to
the P.C. BOARD which in turn activates an
electronic timer.
DIP SWITCH FACTORY SETTING COMBINATIONS PER MODEL AND VERSION
TAB. A
DIP SWITCH
ACM 85 A
ACM 85 W
ACM 125 A
ACM 125 W
ACM 175 A & W
ACS 225 A & W
ACM 225 A & W
ACL 225 A & W

PRINCIPLE OF OPERATION

How it works

FREEZING CYCLE
1 2 3
ON ON OFF
ON ON OFF
ON ON OFF
OFF ON OFF
OFF OFF OFF
OFF OFF ON
ON ON OFF
OFF OFF OFF
The timer, which is built-in the P.C. BOARD,
takes over from the evaporator temperature
sensor, the control of the freezing cycle up to its
completion.
NOTE. The change of the electric potential of
the evaporator sensor with the consequent
activation of the timer (Time mode) is signalled
by the glowing-up of the RED LED located in
the front of the P.C. BOARD.
ATTENTION. In case, after 15 minutes
from the beginning of the freezing cycle,
the temperature of the evaporator sensor
probe is higher then 0° C (32°F) (shortage
of refrigerant, inoperative hot gas valve,
etc.) the P.C. BOARD switch OFF
immediately
simultaneous blinking of the WARNING
RED LED.
The length of this second portion of the freezing
cycle is pre-fixed and related to the setting of the
first four DIP SWITCH keys.
The DIP SWITCH keys setting is made in
consideration of the type of condenser used.
In Table B are indicated the various lengths of
the second portion of freezing cycle (Time mode)
in relation to the different combinations of the DIP
SWITCH KEYS.
In Table A herebelow are illustrated the DIP
SWITCH keys combinations for the three different
models and versions as they are set in the
factory.
The electrical components in operation during
the freezing cycle are:
COMPRESSOR
FAN MOTOR (in air cooled version)
WATER PUMP
CONTACTOR COIL
and during the second phase of freezing cycle
(Time mode) they are joined by the
ELECTRONIC TIMER
DEFROST CYCLE
4
5 6
ON ON ON
ON OFF OFF
ON ON ON
ON OFF OFF
ON ON ON
ON OFF OFF
ON OFF ON
ON OFF OFF
the unit with the
DIAGN. W.PUMP KWD
7 8 9
OFF OFF ON OFF
ON OFF ON OFF
OFF OFF ON OFF
ON OFF ON OFF
OFF OFF ON OFF
ON OFF ON
ON OFF ON
ON OFF ON
10
ON
ON
ON