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Sealed System
Basic Components
The basic components of a refrigerated unit are a
compressor, condenser, evaporator, heat exchanger
(capillary tube and suction line), drier and perimeter hot
tube.
Perimeter Hot Tube
To reduce the possibility of condensation forming on the
exterior of the cabinet in high humidity areas, a perimeter
hot tube (refrigerant tube) has been installed in the unit.
The perimeter tube extends up the left side, across the
top of the unit and down the right side into the filter drier.
When the compressor operates, warm refrigerant flows
through the primary condenser, then into the primary hot
tube, warming the cabinet front exterior.
The perimeter hot tube is not replaceable. In the unlikely
event of a leak in the hot tube, a kit is available to
bypass the hot tube in the sealed system. An electrical
heater wire must be installed within the tubing. The
electrical connection for the electrical heater wire for a
solid state PTC relay compressor is be connected into
the condenser fan circuit. For a variable speed
compressor, the electrical connection must be made to
the 115V inverter board. Refer to the appropriate parts
list of the model being serviced for the correct kit part
number.
Refrigerant Cycle
The refrigerant cycle is a continuous cycle that occurs
whenever the compressor is in operation. Liquid
refrigerant is evaporated in the evaporator by the heat
that enters the cabinet through the insulated walls, and
by the heat from product load and door openings. The
refrigerant vapor is then drawn from the evaporator,
through the suction line, to the compressor.
Compression raises the pressure and temperature of the
vapor in the compressor and the vapor is then forced
through the discharge valve into the discharge line and
into the condenser. Air passing over the condenser
surface removes heat from the high pressure vapor
which then condenses to a liquid. The liquid refrigerant
then flows from the condenser to the evaporator through
the small diameter liquid line (capillary tube).
Before it enters the evaporator, the liquid refrigerant is
sub-cooled in the heat exchanger by the low temperature
suction vapor in the suction line. When refrigerant is
added, the frost pattern will improve, the suction and
discharge pressures will rise, the condenser will become
hot and the wattage will increase.
Testing for Refrigerant Leaks
The line piercing valve (clamp-on type) should be
used for test purposes only. It must be removed
from system after it has served its purpose.
If the sealed system is diagnosed as short of refrigerant
and the system has not been recently opened, there is
probably a leak in the system. Adding refrigerant without
first locating and repairing the leak or replacing the
component will not permanently correct the difficulty.
The leak must be found!
Sufficient refrigerant may have escaped to make it
impossible to leak test effectively. In such cases, add a
¼" line piercing valve to the compressor process tube.
Add sufficient refrigerant vapor to increase the pressure
to 75 lbs. per sq. in. Through this procedure, leaks are
more easily detected before discharging the system into
reprocess/recapture equipment. Check the low side for
leaks. Run the compressor 2 or 3 minutes and check
the high side for leaks. Recover refrigerant using an
EPA approved recovery system.
Checking For Internal Leaks
Before checking for internal leaks, check all accessible
system components and joints for leaks.
If an internal leak is suspected, it must be confirmed.
Use the following procedure:
1. Discharge the system by using refrigerant recovery
equipment.
2. Disconnect the condenser and the drier from the hot
tube on refrigerators. On food freezers, separate the
high and low pressure sides of the system. Pinch off
and solder closed one end of the part of the system
to be tested.
3. Solder a 1/4" charging hose fitting to the open end of
the part of the system to be tested.
4. Connect a pressure gauge and access valve to the
open end of the part of the system to be tested.
Pressurize to 250 lbs. using dry nitrogen or carbon
dioxide.
5. Leave the pressure on the hot tube for 24 hours.
Any drop in pressure is an indication of a leak.
5-4
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