Scroll Compressor Functional Check - Emerson Copeland Scroll Digital ZPD34 Bulletin

Copeland Scroll Compressor Functional Check
A functional compressor test with the suction service
valve closed to check how low the compressor will pull
suction pressure is not a good indication of how well a
compressor is performing. Such a test may damage a
scroll compressor. The following diagnostic procedure
should be used to evaluate whether a Copeland Scroll
compressor is working properly.
1. Proper voltage to the unit should be verified.
2. The normal checks of motor winding continuity
and short to ground should be made to determine
if the inherent overload motor protector has
opened or if an internal motor short or ground fault
has developed. If the protector has opened, the
compressor must be allowed to cool sufficiently
to allow it to reset.
3. Proper indoor and outdoor blower/fan operation
should be verified.
4. Remove power from the unloader solenoid to
load the compressor 100% . 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 in the
system.
5. If suction pressure does not drop and discharge
pressure does not rise to normal levels, reverse
any two of the compressor power leads (this
procedure is for 3-phase compressors only) and
reapply power to make sure compressor was not
wired to run in reverse direction. If pressures still
do not move to normal values, either the reversing
valve (if so equipped) or the compressor is faulty.
Reconnect the compressor leads as originally
configured and use normal diagnostic procedures
to check operation of the reversing valve.
The solenoid coil should only be energized
when it is installed on the solenoid valve.
Energizing the coil when it is not installed on
the valve will result in a failed coil.
Note: It is also possible that the unloader valve is
not closed. With the compressor off, cycle power
to the unloader solenoid and listen for clicking. If
no sound is heard the valve is very likely stuck.
6. To test if the compressor is pumping properly,
the compressor current draw must be compared
to published compressor performance curves
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using the operating pressures and voltage of
the system. If the measured average current
deviates more than ±15% from published values,
a faulty compressor may be indicated. A current
imbalance exceeding 15% of the average on the
three phases should be investigated further. A
more comprehensive trouble-shooting sequence
for compressors and systems can be found in
Section H of the Emerson Electrical Handbook,
Form No. 6400.
7. Before replacing or returning a compressor: Be
certain that the compressor is actually inoperable.
As a minimum, recheck a compressor returned
from the field in the shop or depot for Hipot,
winding resistance, and ability to start before
returning. More than one-third of compressors
returned to Emerson for warranty analysis are
determined to have nothing found wrong. They
were misdiagnosed in the field as being inoperable.
Replacing working compressors unnecessarily
costs everyone.
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AE4-1395 R5