Vogt P118F/HE100, Service Manual

Page: 45 / 126

05TA Service Manual
START-UP AND OPERATION
7/19/13
5-1
5. Start-Up and Operation
Refrigeration System Review.
The refrigeration system uses R-22 or R-404a refrigerant, a
compressor, a refrigerant float switch, a flooded evaporator (freezer), and warm gas defrost.
Following the schematic, notice that during the freeze period of the machine’s cycle, the compressed
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, the thawing
chamber (a lower separate section of the freezer) and the liquid feed solenoid valve (the “A” valve).
The opening of the “A” valve by the float switch during the freeze cycle allows the liquid to be
metered by the hand expansion valve (17). The “A” valve opens and closes in response to the float
switch and 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 contacts to close, initiating the harvest period.
During the harvest period, the liquid feed solenoid valve (“A” valve) closes and the thawing gas
solenoid valve (the “D” valve) is open allowing the warm high pressure gas to enter the freezer. This
heat warms the tubes, allowing the ice to release and slide down onto the rotating cutter. This thaw
period lasts approximately 2 1/2 minutes.
Refrigerant Charge.
Included with the machine is the required charge (approximately 250 lbs.) of
Refrigerant 22 or 404a, depending on the model, 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.
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.