Application Engineering
B U L L E T I N
AE4-1374 R1
To avoid disruption of operation, an electronic control
that can sense brief power interruptions may be used
to lock out the compressor for a short time. This control
could be incorporated in other system controls (such
as defrost control board or the system thermostat), or
can be a stand-alone control. Functional specifications
for this control as well as a suggested wiring diagram
are shown in Figure 3. No time delay is necessary for
three phase models since the motor starting torque is
high enough to overcome reverse rotation.
APPLICATION TESTS
Application Test Summary
There are a minimal number of tests the system
designer will want to run to ensure the system operates
as designed. These tests should be performed during
system development and are dependent on the system
type and amount of refrigerant charge. These application
tests are to help identify gross errors in system design that
may produce conditions that could lead to compressor
failure. The Continuous Floodback Test and Field
Application Test, both outlined below, are two tests to
run to help verify the design. When to run these tests
can be summarized as follows:
Continuous Floodback:
Required on all air-source heatpumps.
Field Application Test:
Required for any unit where both the design system
charge is higher than the compressor refrigerant
charge limit listed in Table 4; 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. Running a partially
blocked indoor air filter or loss of evaporator air flow test
and comparing the sump temperature results to Figure
1 is recommended. 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
© 2013 Emerson Climate Technologies, Inc.
Printed in the U.S.A.
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 compressor
sump temperature must remain above the sump
temperature shown in Figure 1 or design changes
must be made to reduce the amount of flood back. If an
accumulator is used, this test can be used to test the
effectiveness of the accumulator. 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 1. 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 1. 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 4. The
criteria for pass/fail is whether the liquid level reaches
the suction tube level. Liquid levels higher than this can
allow refrigerant/oil to be ingested by the scrolls and
pumped out of the compressor after start-up.
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