Electrical Sequence - Scotsman NM650 Service Manual

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 compressor relay and auger motor
relay become energized, connecting power
to the windings of the auger motor.
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 stay 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 bin
empty light goes out, and the machine
shuts down.
Shut Down consists of:
The compressor relay 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 switch)
opens, the machine will stop immediately
(through the relays on the circuit board). It
must be manually reset at the control.
If the low pressure control (cut out switch)
opens, the machine will stop immediately
(through the relays on the circuit board). It
must be manually reset at the control.
If the spout switch opens, the machine will
stop immediately (through the relays on the
circuit board) It must be manually reset.
Older models (late 1990 production and
before) The reset switch on the circuit
board must be manually reset if either of
the pressure switches opens or if the spout
switch opens (early spout switch was a
automatic reset).
The master switch is the manual control for
the complete machine, but it is not a
service disconnect.
January, 1991
Page 13
NM650