Liebert CHALLENGER 3000 - Manual (Page 59)

Component Operation and Maintenance
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6.4.8 Compressor Functional Check
The following diagnostic procedure should be used to evaluate whether the 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. Condenser glycol flow should
be verified.
4. 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 and reapply power to make sure compressor was not wired
to run in reverse direction. If pressures still do not move to normal values, system is properly
charged and solenoid valves function, the compressor is faulty. Reconnect the compressor leads as
originally configured and use normal diagnostic procedures to check operation of the reversing
valve.
6. To test if the compressor is pumping properly, the compressor current draw must be compared to
published compressor performance curves 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.
7. Before replacing or returning a compressor: Be certain that the compressor is actually
defective. At 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 for warranty analysis are determined to have nothing wrong. They were
misdiagnosed in the field as being defective. Replacing working compressors unnecessarily costs
everyone.
6.4.9 Compressor Replacement
Infrequently a fault in the motor insulation may result in a motor burn, but burnouts rarely occur in
a properly installed system. Of those that do, most are the effects of mechanical or lubrication fail-
ures, resulting in the burnout as a secondary consequence.
If problems that can cause compressor failures are detected and corrected early, a large percentage
can be prevented. Periodic maintenance inspections by alert service personnel on the lookout for
abnormal operation can be a major factor in reducing maintenance costs. It is easier and far less
costly to take the steps necessary to ensure proper system operation than it is to allow a compressor
to fail and require replacement.
When troubleshooting a compressor, check all electrical components for proper operation.
1. Check all fuses and circuit breakers.
2. Check Hi-Lo Pressure switch operation.
3. If a compressor failure has occurred, determine whether it is an electrical or mechanical failure.
Mechanical Failure
A mechanical compressor failure will be not be indicated by a burned odor. The motor will attempt to
run. If you have determined that a mechanical failure has occurred, the compressor must be replaced.
If a burnout does occur, correct the problem that caused the burnout and clean the system. It is
important to note that successive burnouts of the same system are usually caused by improper clean-
ing.