12
© 2016 Emerson Climate Technologies, Inc.
AE4-1303 R15
charge is higher than the compressor refrigerant
charge limit listed in
Table 5
; and a capillary tube,
fixed orifice, or bleed-type TXV is used on either the
indoor or the outdoor coil of the unit.
Continuous Floodback Test
It is expected that the design would not flood during
standard air conditioning operation. Flooding during
defrost cycles should be minimal and the flow control
device must regain control of the refrigerant flow after
the defrost cycle to ensure suction gas superheat. The
use of a TXV in heating does not guarantee operation
without flood back in the lower end of the unit/TXV
operating range.
To test for excessive continuous liquid refrigerant flood
back, it is necessary to operate the system in a test
room at conditions where steady state flood back may
occur (low ambient heating operation). Thermocouples
should be attached with glue or solder to the center of
the bottom shell and to the suction and discharge lines
approximately 6 inches (15 cm) from the shell. These
thermocouples should be insulated from the ambient air
with Permagum™ or other thermal insulation to be able
to record true shell and line temperatures. If the system
is designed to be field charged, it should be overcharged
by 15% in this test to simulate overcharging often found
in field installations.
The system should be operated at an indoor
temperature of 70°F (21°C) and outdoor temperature
extremes of 10°F (-12°C) or lower in heating to produce
flood back conditions. The compressor suction and
discharge pressures and temperatures as well as the
sump temperature should be recorded. The system
should be allowed to frost up for several hours (disabling
the defrost control and spraying water on the outdoor
coil may be necessary) to cause the saturated suction
temperature to fall below 0°F (-18°C). The suction
superheat must remain positive or design changes must
be made to increase suction superheat and reduce
flooding. Increasing indoor coil volume, increasing
outdoor air flow, reducing refrigerant charge, decreasing
capillary or orifice diameter, and adding a charge
compensator can also be used to reduce excessive
continuous liquid refrigerant flood back.
Field Application Test
To test for repeated, excessive liquid flood back
during normal system off-cycles, perform the
Field
Application Test
that is outlined in
Table 2
. Obtain a
sample compressor with a sight-tube to measure the
liquid level in the compressor when it is off.
Note: The sight-tube is not a good liquid level indicator
when the compressor is running because the top of
the sight-tube is at a lower pressure than the bottom
causing a higher apparent oil level.
Set the system up in a configuration with the indoor
unit elevated several feet above the outdoor unit with
a minimum of 25 feet (8 meters) of connecting tubing
with no traps between the indoor and outdoor units. If
the system is designed to be field charged, the system
should be overcharged by 15% in this test to simulate
field overcharging. Operate the system in the cooling
mode at the outdoor ambient, on/off cycle times, and
number of cycles specified in
Table 2
. Record the
height of the liquid in the compressor at the start of
each on cycle, any compressor overload trips, or any
compressor abnormal starting sounds during each
test. Review the results with Application Engineering
to determine if an accumulator or other means of off
cycle migration control are required.
This test does
not eliminate the requirement for a crankcase
heater if the system charge level exceeds the
values in Table 5
. The criteria for pass/fail is whether
the liquid level reaches the bottom of the terminal box.
Liquid levels higher than this can allow refrigerant/oil
to be ingested by the scrolls and pumped out of the
compressor after start-up.
The tests outlined above are for common applications
of compressors in this family. Many other applications
of the compressor exist, and tests to insure those
designs can’t possibly be covered in this bulletin.
Please consult with Application Engineering on
applications outside of those outlined above for the
appropriate application tests.
ASSEMBLY LINE PROCEDURES
Compressor Handling
WARNING
Use care and the appropriate material handling
equipment when lifting and moving compressors.
Personal safety equipment must be used.
Because oil might spill out of the suction connection
located low on the shell, the suction connection plug
must be left in place until the compressor is set into the
unit. If possible, the compressor should be kept vertical
during handling. The discharge connection plug should
