Scotsman NU150 Service Manual page 21

NU Undercounter Ice Machine Service Manual
High Pressure Control switch
The high Pressure Control is in the ice machine,
when the ice machine occurs failure and the
high pressure is more than 33bar(462psi), the
high pressure control switch will cut off the
electricity supply to protect the ice machine.
The indicator lights ZBLX+R1LX will be keeping
blink (on the PC board, light SL1 will bright.)
until the high pressure lowers to 23bar (322psi),
then can restart the ice machine.
Water temperature sensor
The water temperature sensor, located in the
water pipes from the water pump to the ice
plate, is used to detect the temperature of
circulating water in real time and sent signals to
PC board with which controls the operation of
pump during the ice making cycle.
Thermostatic Expansion Valve
The Thermostatic Expansion Valve regulates
the flow of refrigerant to the evaporator and
reduces pressure of liquid refrigerant from
condensing pressure to evaporating pressure.
This drop in pressure causes the refrigerant to
cool. The cooled refrigerant absorbs heat from
the water circulating over the evaporator. As
the evaporator fills with liquid refrigerant, the
evaporator becomes colder.
The flow of refrigerant into the evaporator is
controlled by the temperature at the outlet of
the evaporator. The expansion valve bulb,
mounted to the top of the suction pipe, senses
the evaporator outlet temperature causing the
expansion valve to open or close.
As ice forms on
temperature drops and the flow of refrigerant
into the evaporator decreases, resulting in a
drop in suction pressure.
The evaporator should become completely
flooded (filled with liquid refrigerant) during the
freezing cycle. Only a completely flooded
evaporator will have a uniform freeze pattern
(ice forms across the evaporator). A starved
evaporator (not enough liquid refrigerants) will
have poor or have no ice formation, the outlet
tube(s) exiting the evaporator will also not frost.
All tubes should frost approximately 5 minutes
from the start of the freezing cycle.
the evaporator, the
An expansion valve that is restricted or not
opening properly will starve the evaporator
resulting in lower than normal suction pressure.
A low refrigerant charge will also starve the
evaporator and
discharge pressures. If not sure the amount
refrigerant in the system, retrieve it back and
recharge of the correct amount of refrigerant
and then re diagnosis whether the valve is
defective.
If the evaporator is starved but the suction
pressure is higher than normal, it shows the
TXV is good; If the TXV keeps open or if the
thermal bulb doesn't contact well with the
suction pipe, the flow of refrigerant into the
evaporator will be too much and the liquid
refrigerant will flood the compressor. The
suction pressure will be higher than normal; the
formation of ice is uniform, but the ice making
cycle will become longer.
symptoms issue
Evaporator the
flooded but bulb of TXV
suction pressure doesn't
not dropping. contact
Compressor has with
been checked suction pipe
and appears
well. TXV
installed
Suction pipe at incorrect
compressor may
be colder than System
normal overcharged
Evaporator Machine
starved, no frost on refrigerant
on pipe(s) charge
exiting
evaporator, TXV restricted
suction pressure or stuck
is low.
Air filter
The NU series air cooled ice machine is
equipped with air inlet filter. As the ice machine
runs, part of dust will be sucked in the machine
through the filter, thus it cuts down the air
volume to be sucked in and then the efficiency
of the ice machine.
20
Components Description
cause low suction
corrections
thermal Tighten bulb clamp,
and confirm that the
insulation is good.
well Put the
the bulb on the top of
suction
Recharge
bulb is refrigerant,
replace the TXV.
low Retrieve
recharged
refrigerant back and
recharge
correct amount of
refrigerant
Replace TXV and
dry filter
and
thermal
pipe.
the
and
the
of the