Scotsman FME1200R Service Manual page 20

NME950R & FME1200R
OPERATION: Refrigeration
The refrigeration system under low condenser air
temperatures is much the same as it is under
higher temperatures, with the exception that the
resulting low head pressures cause the head
pressure control to close off the liquid line between
the condenser and the receiver. This forces more
SCHEMATIC OF DISCHARGE PRESSURE
CONTROL VALVE, Normal Temperature
From
Compressor
From
Condenser
OPERATION: Refrigeration
During the pump down cycle (usually initiated by
the circuit board de-energizing the liquid line valve)
the discharge gases flow through their normal path
to the remote condenser, through the head
pressure control, and into the receiver. At this
point the refrigerant flow is stopped by the closed
liquid line valve. This action forces the refrigerant
into the receiver and keeps it out of the
compressor. The pump down continues until the
low pressure control turns the compressor off.
Low Condensing Temperature
Valve
Disk
To Receiver
PUMP DOWN
December 1995
Page 20
refrigerant into the condenser (with a small amount
of discharge gas going into the receiver to
maintain pressure until the head pressure is built
back up to the rated gauge pressure of 180 psig).
At that pressure the valve opens up the liquid line
from the condenser to the receiver.
SCHEMATIC OF DISCHARGE PRESSURE
CONTROL VALVE, Low Temperature
From
Compressor
From
Condenser
To Receiver