Operation - Scotsman UF424A-1A Technical Manual

UF424 / UN324 Technical Manual

Operation

At initial start up there is no ice in the ice storage bin, so there is nothing blocking the infrared sensors that are
used to control the on or off mode of the machine. A push of the on off button triggers the controller to begin ice
making.
The controller checks for water using the continuity sensor in the reservoir. If that sensor indicates there is
water, and the refrigeration pressure switch is closed, the controller connects power to the compressor, fan
motor (if air cooled) and auger drive motor.
The compressor forces refrigerant to circulate causing the evaporator to become very cold, which takes heat
from the water inside the evaporator's tube. That refrigerated space also contains the slowly rotating auger.
Eventually enough heat is removed from the water to cause ice crystals to form. When enough ice crystals
have formed the auger moves them vertically up the tube and the soft, wet ice is forced through the slots in
the ice breaker. The limited area of the slots causes the soft ice to be forced together, forming either flaked or
nugget ice, depending upon the design of the breaker. As ice exits the breaker or extruder, more water flows
from the reservoir into the bottom of the evaporator tube.
Water replenishment by the gravity fed water is the key element in this ice making process. It provides a
continuous heat load to the refrigeration system so that, as ice is made, an equal amount of water re-enters the
system, keeping the system in balance. A flaker then, is a unique refrigeration system in that it is steady-state.
Once the machine has begun to make ice the evaporator's temperature does not change as the replenished
water keeps adding heat.
The ice slides down a chute into the insulated bin. The bin is not refrigerated. There is a drain at the bin's floor
to let melt water out. As it is made, ice will pyramid under the chute and form a pile that gradually increases to
the point that the top of the pile enters the chute, blocking the infrared light between the ice sensor's emitter
and receiver, which signals the controller to stop making ice. The ice level at the first shut off may be less than
later when the bin temperature has stabilized. Ice storage bin capacities are calculated by the bin's internal
volume, so the amount of available ice may not equal the calculated quantity unless ice is distributed to the
sides during use.
The shut off process begins when the controller opens the compressor relay, cutting the power to the
compressor. The auger motor continues to operate to clear the evaporator tube of any ice that was in it. Then it
is shut off. In normal operation when the ice is used or melts enough to expose the emitted infrared light to the
sensor's receiver, and the compressor has been off for the preset amount of time, ice making will restart.
Sound
The normal sounds of this machine are the compressor, fan blade if air cooled, and auger drive motor.
Occasionally there may be a slight crunching sound as ice is forced thru the extruder or breaker. A loud
moaning noise could occur if ice is not sliding vertically up the evaporator tube. If it revolves with the auger,
it will remain under refrigeration too long, and could even freeze to the evaporator wall. Then it becomes like
chipped ice, which causes the gear reducer to be overloaded as it pushes the extra hard ice thru the extruder.
That is known as a rotating freeze. The most likely cause of a rotating freeze is internal scale build up,
especially on the auger.
September 2017
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