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Flake Ice Machines Refrigeration System
Page F11
Mixing Valve Diagnosis:
Problem Possible Cause Remedy
Pump Down System (Remote Only)
a. Replace valve
a. Leak check. Recover
refrigerant and weigh
in proper charge.
b. Replace valve.
a. Replace valve.
a. Valve defective, not
allowing discharge
gas into receiver
a. System low on
charge.
b. Valve defective, not
allowing liquid into
receiver.
a. Valve defective, not
allowing refrigerant
through condenser.
1. Head pressure low,
Line between valve
and receiver cold.
Ambient condenser
temp. below 70°F
(21°C)
2. Head pressure low,
Line between valve
and receiver hot.
3. Head pressure low,
Line returning from
condenser is cool.
Ambient condenser
temperature is above
70°F
(
21°C
)
The pump down system prevents liquid refrigerant from migrating to the evaporator and
compressor during the off cycle and prevents the compressor from slugging or starting under
an excessive load.
Liquid Line Solenoid
When a machine with a remote condenser shuts off, the liquid line
solenoid valve, located at the outlet of the receiver, is de-energized
causing the valve to close completely restricting the flow of refrigerant.
The compressor will pump all of the refrigerant into the condenser and
receiver.
As the system pumps down, the pressure on the low side of the system
drops. When the suction pressure drops to 19 psi (1.3 bar), the pump down control opens
and shuts the machine off. See page G5 for pump down control operation. Liquid refrigerant
is stored in the condenser and receiver while the machine is off. It is normal for the machine
to pump down once or twice an hour as the pressures equalize.
When the machine comes back on (the bin switch closes or the selector switch placed to the
ICE position), the liquid line solenoid valve opens and the refrigerant is released from the
receiver. When the suction pressure rises to 45 psi (3.1 bar) the pump down control closes
and the machine comes back on. If the machine will not pump down, the valve may not be
closing all the way. A weak compressor will also prevent the machine from pumping down.
Check for signs of a weak compressor before replacing the liquid line solenoid. Prior to
replacing the valve, disassemble and check for obstructions that may not allow the valve to
seat.