How It Works; Electrical Sequence - Air Or Water Cooled - Scotsman MVP456 Service Manual

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HOW IT WORKS - AIR COOLED
Freeze Cycle. At start up the controller drains
and refills the reservoir. The reservoir refills
when the mid length water level sensor probe is
uncovered and continues to fill until the top probe
is in contact with water. When the reservoir has
filled, the compressor and water pump start.
After the discharge pressure has increased past
the cut in point of the fan pressure control, the fan
motor(s) will begin to operate and warm air will be
discharged out the back of the cabinet. The fan
motor will switch on and off as the discharge
pressure rises and falls. Water flows over the
evaporator as the refrigeration system begins to
remove heat. When the water temperature falls
to a preset point, as measured by the water
temperature sensor, the controller shuts off the
water pump for 30 seconds. The freeze cycle
resumes when the pump restarts and ice begins
to form on the evaporator. As it forms, the water
flowing over the ice moves closer and closer to
the metal tip of the ice thickness sensor. When it
comes into contact with the sensor for a few
continuous seconds, that signals the controller
that the freeze cycle is complete.
The controller may shut the air cooled fan motor
off for a variable period of time to build up heat for
harvest. This is dependant upon the temperature
of the discharge line sensor.
Harvest Cycle. When the harvest cycle begins,
the controller shuts off the fan motor, switches on
the hot gas valve, and through a parallel circuit,
the harvest assist solenoid. After a few seconds
the purge valve opens and water is drained from
the reservoir. Based on either the automatic
purge or manual purge setting, the pump and
purge valve will be switched off at a time
determined to have drained enough water for
that setting. The inlet water valve will open to fill
the reservoir anytime the mid length probe is
uncovered, which occurs during the reservoir
drain cycle. Harvest continues as the hot
discharge gas flows into the evaporator
serpentine, heating up the evaporator. At the
same time the harvest assist solenoid is pushing
against the back of the ice slab. When the ice
releases from the evaporator, it harvests as a
unit, and the harvest assist probe provides some
additional force to push it off. When the ice falls
off it will force the curtain open. An open curtain
during the harvest cycle signals the controller
that the evaporator has released its ice terminating
harvest. If the curtain remains open, the controller
will shut the machine at bin full. Anytime harvest
is complete the hot gas valve and harvest assist
solenoid are shut off. The harvest assist solenoid
pin returns to its normal position by spring
pressure.
If the curtain re-close after harvest, the freeze
cycle will restart.
HOW IT WORKS - WATER COOLED
Freeze Cycle. At start up the controller drains
and refills the reservoir. The reservoir refills
when the mid length water level sensor probe is
uncovered and continues to fill until the top
probe is in contact with water. When the reservoir
has filled, the compressor and water pump start.
After the discharge pressure has increased past
the set point of the water regulating valve, the
water regulating valve will open and warm water
will be discharged out the condenser drain. The
water regulating valve will modulate to maintain
a relatively constant discharge pressure. Water
flows over the evaporator as the refrigeration
system begins to remove heat. When the water
temperature falls to a preset point, as measured
by the water temperature sensor, the controller
shuts off the water pump for 30 seconds. The
freeze cycle resumes when the pump restarts
and ice begins to form on the evaporator. As it
forms, the water flowing over the ice moves
closer and closer to the metal tip of the ice
thickness sensor.
When it comes into contact with the sensor for a
few continuous seconds, that signals the
controller that the freeze cycle is complete.
Harvest Cycle. When the harvest cycle begins,
the controller switches on the hot gas valve, and
through a parallel circuit, the harvest assist
solenoid. After a few seconds the purge valve
opens and water is drained from the reservoir.
Based on either the automatic purge or manual
purge setting, the pump and purge valve will be
switched off at a time determined to have drained
enough water for that setting. The inlet water
valve will open to fill the reservoir anytime the
mid length probe is uncovered, which occurs
during the reservoir drain cycle. Harvest
continues as the hot discharge gas flows into the
evaporator serpentine, heating up the evaporator.
At the same time the harvest assist solenoid is
pushing against the back of the ice slab. When
the ice releases from the evaporator, it harvests
as a unit, and the harvest assist probe provides
some additional force to push it off. When the ice
falls off it will force the curtain open. An open
curtain during the harvest cycle signals the
controller that the evaporator has released its ice
terminating harvest. If the curtain remains open,
the controller will shut the machine at bin full.
Anytime harvest is complete the hot gas valve
and harvest assist solenoid are shut off.
The harvest assist solenoid pin returns to its
normal position by spring pressure.
If the curtain re-close after harvest, the freeze
cycle will restart.
ELECTRICAL SEQUENCE
Air or Water Cooled
Power connected, unit previously switched Off.
Control board does a self check. If the self check
fails, the unit displays an E and no further action
will occur.
If the self check passes, the controller will display
a 0, the curtain light will be ON and the Power
and Sump Empty lights will be ON.
Pushing and releasing the On button will start
the ice making process.
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