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Adjust the refrigerant charge until to a sub-cooling of 8 to 10° F and has sparse bubbles. The unit
should be allowed to stabilize for several minutes before meaningful measurements can be taken.
A properly charged system operating at typical parameters will have the following pressures:
Units with R-407C Head pressure 240 – 295 PSIG
Suction Pressure 52 PSIG or greater
Units with R-410A Head pressure 340 – 415 PSIG
Suction pressure 104 – or greater
The superheat at the compressor suction line should be 8 – 15 degrees. Sub-cooling should be
8 – 10° F.
NOTE: Charging to a full liquid line sight-glass should never be the sole means of de-
termining the correct refrigerant charge. Other parameters such as superheat, suction
pressure, head pressure, sub-cooling and ambient temperature are also important. A
system charged to a clear sight-glass is often overcharged.
4.2.2 Flooded System Charging
Flooded systems include an optional liquid receiver and head pressure control valve for use primar-
ily in colder climates. When the ambient temperature falls during cold weather, the head pressure
control valve will regulate the fl ow of refrigerant to ensure nearly constant receiver pressure. The
receiver is partially fl ooded with liquid refrigerant in cold weather. In warm weather the extra refrig-
erant is stored in the receiver.
Flooded systems require more refrigerant than units with fan speed control. Connect the pressure
gauge manifold set to the high and low ports near the compressor. Connect the charging line to
the refrigerant tank and set it for liquid feed. Open the refrigerant tank valve and purge the line at
the manifold. Open the high side valve on the manifold only and allow the refrigerant to fl ow until
the system pressure equalizes. At this point the system will have 75 to 85% of the total refrigerant
charge. Start the evaporator blower. Start the compressor and check the operating pressures and
temperatures.
A quick and easy way to run the blower and compressor is by using the manual switches provided
with the microprocessor (located in the control module). Switch the blower and compressor manual
switches to the ON position. All automatic control is disabled but safety switches will remain func-
tional.
WARNING: Before starting a compressor, the crankcase heater should be energized
for a minimum of 12 hours to reduce the possibility of liquid slugging on start-up. Failure
to energize the crankcase heater could result in compressor damage. If the system is
charged from a vacuum, the pre-heating of the compressor is not necessary.
Start the evaporator fan and verify the fan rotation. Start the compressor. Check the liquid line
sight-glass to get a feel for the approximate charge. Bubbles in the sight-glass are not unusual at
this point and can be caused by fl ashing from liquid pressure drop, low sub-cooling or low charge.
It is likely more refrigerant will be required to complete the charging procedure.
(39 paginas)
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