Electrical Sequence - Scotsman NM1250R Service Manual

NM1250R

ELECTRICAL SEQUENCE

Refer the wiring diagram as needed.
If the machine is switched off at the master
switch, but is otherwise ready to go, switching
the master switch to ON does the following:
The bin empty light on the circuit board
goes on
There is a 15 second delay
If there is enough water in the reservoir, the
circuit board will allow the machine to start
up.
Start up consists of:
The liquid line relay and auger motor relay
become energized, connecting power to the
liquid line solenoid coil and the windings of
the auger motor.
The liquid line solenoid opens, raising the
low side pressure.
The pump down control closes
The auger motor starts, and the centrifugal
switch closes, connecting power to the
compressor contactor coil.
The contactor is energized, connecting
power to the compressor, and the
compressor starts.
As ice goes past the ice level sensors, the
bin empty light will be on and the machine
will continue to run, unless the ice stays
between the sensors for more than 15
seconds (bin full). At that point, the
machine shuts down.
Shut Down consists of:
The liquid line solenoid relay opens,
lowering the suction pressure.
The pump down pressure control opens.
The compressor contactor opens
The compressor stops
The auger motor is run by the circuit board
for 2.5 more minutes, clearing out ice in the
evaporator, and then
The auger motor relay opens, and the
auger motor stops.
If the ice level sensor is clear (bin empty) for
more than 15 seconds, the machine will start
up again.
Another purpose of the circuit board is to turn
the machine off if there is not enough water in
the machine.
When the water level in the reservoir falls
below the water level sensor, the machine
will "shut down"
When the water refills the reservoir, the
machine will start up again.
Separate from the circuit board:
If the high pressure control (cut out) opens,
the machine will stop immediately (through
the relays on the circuit board) and cause
the reset switch on the circuit board to light
up. It must be manually reset at the control
and at the reset switch on the circuit board.
The pump down control switch will stop &
start the compressor.
If the spout switch opens the machine will
stop immediately (through the relays on the
circuit board) and cause the reset switch on
the circuit board to light up. It is a manual
reset at the circuit board.
The master switch is the manual control for
the complete machine, but it is not a service
disconnect.
November, 1988
Page 18