Vogt P18FXT Service Manual Download

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10TA Service Manual

START-UP AND OPERATION

4/14/14

5-1

Start-Up and Operation

Refrigeration System Review

The refrigeration system uses R-22 or R-404a refrigerant, a

compressor, a refrigerant float switch, expansion valve, 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 thawing chamber (a
lower separate section of the freezer) then the filter/drier.  The liquid feed solenoid valves (“A1” and
“A2”) being open during the freeze cycle allows the liquid to be metered by the float switch as the
“A1”  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 500 lbs.) of

Refrigerant  (R-22  or  R-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.
They should indicate a pressure approximately equal to the ambient temperature.  This pressure can
be found using the pressure temperature chart for the applicable refrigerant, TABLE 11-7.

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.