Vogt TUBE-ICE P-118F, Service Manual

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P118F Service Manual
START-UP AND OPERATION
1/6/09
5-1
5. Start-Up and Operation
Refrigeration System Review.
The refrigeration system uses R-404a refrigerant, a compressor, a
refrigerant float switch, a flooded evaporator (freezer), and warm gas defrost. Following the
schematic, you see that during the freeze period of the machine’s cycle, the condenser discharge gas
leaves the compressor and goes to the condenser where it is condensed into liquid by the removal of
heat by either air or water passing through the condenser. A reservoir of liquid is accumulated in the
receiver and flows as required, passing through the filter/drier then the thawing chamber (a lower
separate section of the freezer). The liquid feed solenoid valve (“A”) being open during the freeze
cycle allows the liquid to be metered by the float switch as the “A” valve opens and closes in
response to the refrigerant level in the freezer. Wet refrigerant floods the evaporator and is in
contact with the outside of the ice-making tubes in which water is being circulated. The heat
contained in this water passes through the wall of the tubes, lowering the temperature of the water,
causing it to freeze and form a long tube of ice that adheres to the inside of each of the freezer tubes.
The flowing water keeps the accumulated ice clear by washing separated solids down into the sump
area of the water tank.
The wet suction gas leaves the freezer and any remaining liquid droplets are removed by the
accumulator and suction line heat exchanger. The dry gas enters the compressor and is compressed
then discharged to the condenser completing the cycle.
As the ice is formed in the freezer, the suction pressure steadily reduces until it causes the freezer
pressure switch to close, initiating the harvest period.
During the harvest period, the thawing gas solenoid valve, (the “D” valve), is open allowing the
warm high pressure gas to enter the freezer. This heat melts a thin film from the outside of the ice,
reducing the diameter and letting it fall free from the freezer tubes. This period lasts approximately
2 1/2 minutes.
Refrigerant Charge. Included with the machine is the required charge (approximately 250 lbs.) of
Refrigerant 404a, which has been isolated in the receiver (15R). Before shipment of the machine,
the compressor service valves (34), (35), and the stop valves in the various lines to the condenser
and receiver have been closed. These valves are tagged with instructions that the valves are to be
opened prior to start-up of the machine. Before opening these valves, it is advisable to check all
joints for leaks that may have developed during shipment. If no leaks are present, a positive
pressure should show on the suction and discharge pressure gages. They should indicate a pressure
approximately equal to the ambient temperature. This pressure can be found using the pressure
temperature chart for R-404a, TABLE 10-7.
If it should ever become necessary to add refrigerant to the system, charging valve (28) is provided
for this purpose. Through this valve, refrigerant can be added in liquid form. See “Adding
Refrigerant." The compressor crankcase heater must be energized for a minimum of two hours prior
to starting and running the compressor.