Harvest Cycle - Scotsman AC-EC 57 Service Manual

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In Table B are indicated the various lengths of the
timed portion of freezing cycle in relation to the
different combinations of the DIP SWITCH KEYS.
In Table A are illustrated the DIP SWITCH keys
combinations for the 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
and during the second phase of freezing cycle
(Time mode) they are joined by the
ELECTRONIC TIMER
The refrigerant head pressure, at avarage 21 °C
amb. temp., in the course of the freezing cycle,
ranges between 15,5 - 10 bar according to the
model in the air cooled version, being controlled
by the temperature sensor probe located within
the condenser fins.
On the air cooled version, the condenser tempe-
rature sensor, when senses a rising of the
condenser temperature beyond the pre-fixed
limit, changes its electrical resistance and
transmits a low voltage power flow to the Micro
Processor of P.C. BOARD which in turn energizes,
through a TRIAC, the FAN MOTOR.
When the opposite situation occures, i.e. the
condenser temperature gets below the pre-fixed
limit, the temperature sensor changes again its
electrical resistance reducing therefore the current
flow to the P.C. BOARD to cause the fan motor
temporary cut-off.
NOTE. In case the condenser temperature
probe senses that the condenser temperatu-
re has rised to 70 ° C (160 ° F) - on air cooled
versions - or 60 ° C (140 ° F) - on water cooled
versions - for one of the following reasons:
CLOGGED CONDENSER (Air cooled version)
INSUFFICIENT FLOW OF COOLING
WATER (Water cooled version)
FAN MOTOR OUT OF OPERATION (Air
cooled version)
AMBIENT TEMPERATURE HIGHER THEN
40 ° C (100 ° F)
it causes the total and immediate SHUT-OFF
of the machine in order to prevent the unit
from operating in abnormal and dangerous
conditions. When the ice maker stops on
account of this protective device, there is a
simultaneous glowing of the RED LED and
RED LIGHT (STEADY), warning the user of
the Hi Temperature situation. After having
eliminated the source of the condenser hi-
temperature, to restart the machine it is
necessary to switch OFF (wait few seconds)
and switch ON again the unit. The ice machine
resumes its normal operation by going through
the 5 minutes water filling phase.
At the start of the freezing cycle the refrigerant
suction or lo-pressure starts from 3,8 - 7,7 bar
and it declines gradually to 1,8 - 0,6 according to
the ice maker model with the growing of the ice
thickness with the cubes fully formed in the cup
molds. The total length of the freezing cycle
ranges from 20 to 25 minutes.
DEFROST OR HARVEST CYCLE
As the electronic timer has carried the system
throughout the second phase of freezing cycle,
the defrost cycle starts.
ATTENTION. In case the unit is able to
reach 0°C (32°F) evaporating temperature
within 15 minutes, but after 45 minutes
from the beginning of the freezing cycle it
has not yet reached the evaporator tem-
perature of -15°C (5°F) the machine goes
straight into the defrost cycle omitting the
timed portion of the freezing cycle relied to
the setting of the first four DIP SWITCHES.
NOTE. The length of the defrost cycle is
related to the length of the second phase of
freezing cycle T2. (Time to drop the
evaporating temperature from 0 ° C (32 ° F) -
small Red LED blinking - to -15 ° C (5 ° F) small
Red LED ON steady.
I t is possible to extend the length of the defrost
cycle by changing the setting of DIP SWITCH
7 and 8 as shown on table at page 34.
The electrical components in operation during
this phase are:
COMPRESSOR
WATER INLET VALVE
HOT GAS VALVE
WATER DRAIN VALVE (ONLY AC/EC 127-177)
and the
WATER PUMP
on the first 15 seconds.
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. D )
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.
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. At the end
of the defrost cycle, the hot gas valve, the water
inlet valve and the water drain valve close and the
machine starts again a new freezing cycle.
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(Fig.C and D)