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© 2015 Emerson Climate Technologies, Inc.
AE4-1387 R7
through the compressor. This may leave the low side
shell and suction line tubing pressurized. If a brazing
torch is then applied to the low side, the pressurized
refrigerant oil mixture could ignite as it escapes and
contacts the brazing flame. It is important to check both
the high and low sides with manifold gauges before
unbrazing. In the case of an assembly line repair,
remove the refrigerant from both the high and low sides.
Instructions should be provided in appropriate product
literatures and assembly areas.
High Potential (Hipot) Testing
Many of the Copeland brand compressors are
configured with the motor below the compressor. As a
result, when liquid refrigerant is within the compressor
shell the motor can be immersed in liquid refrigerant to
a greater extent than with compressors with the motor
mounted above the compressor. When Copeland brand
compressors are Hipot tested and liquid refrigerant is
in the shell, they can show higher levels of leakage
current than compressors with the motor on top because
of the higher electrical conductivity of liquid refrigerant
than refrigerant vapor and oil. This phenomenon
can occur with any compressor when the motor is
immersed in refrigerant. The level of current leakage
does not present any safety issue. To lower the current
leakage reading, the system should be operated for a
brief period of time to redistribute the refrigerant to a
more normal configuration and the system Hipot tested
again. See bulletin
AE4-1294
for Megohm testing
recommendations. Under no circumstances should
the Hipot or Megohm test be performed while the
compressor is under a vacuum.
SERVICE PROCEDURES
Copeland Scroll
Functional Check
Refrigeration scroll compressors do not have internal
suction valves. It is not necessary to perform functional
compressor tests to check how low the compressor will
pull suction pressure. This type of test may damage a
scroll compressor. The following diagnostic procedure
should be used to evaluate whether a Copeland Scroll
compressor is functioning properly.
1. Verify proper unit voltage.
2. Normal motor winding continuity and short to
ground checks will determine if the inherent
overload motor protector has opened or if an
internal short to ground has developed. If the
protector has opened, the compressor must cool
sufficiently to reset.
3. With service gauges connected to suction
and discharge pressure fittings, turn on the
compressor. If suction pressure falls below
normal levels, the system is either low on charge
or there is a flow blockage.
4a. Single-Phase Compressors
If the suction pressure does not drop and the
discharge pressure does not rise to normal levels
the compressor is faulty.
4b. Three-Phase Compressors
If the suction pressure does not drop and the
discharge pressure does not rise, reverse any two
of the compressor power leads and reapply power
to make sure the compressor was not wired to
run in the reverse direction.
The compressor current draw must be compared to
published compressor performance curves at the
compressor operating conditions (pressures and
voltages). Significant deviations (±15%) from
published
values may indicate a faulty compressor.
NOTICE
Note that the ZS09-19KAE-(TFD, TFE, TF7, TF5) three
phase motors use a modified "Scott-T" connection
and don't have equal resistance on all three windings.
Two windings will have equal resistances and the third
winding will be lower than the other two. See
Figure
A
. Carefully compare measured motor resistance
values to the two different published resistance values
for a given compressor model before replacing the
compressor as being defective. Due to the nature of
the Scott-T construction there is an inherent current
imbalance in the motors that is much larger than what
is seen in a standard 3-phase motor. Effectively you
will have two terminals drawing similar currents while
the third will draw a higher current. The current draw
on the Scott –T motors as shown in the performance
data and in the operating envelope (available online at
www.emersonclimate.com under the Online Product
Information link) comes from the 2 main windings. The
larger ZS21-33KAE compressors have conventional
three-phase motors with equal resistances in each
winding.
