RXB PLUS ROTARY SCREW COMPRESSOR UNITS S70-101 IOM
Page 41
TROUBLESHOOTING GUIDE
Successful problem solving requires an organized approach
to define the problem, identify the cause, and make the
proper correction.
ABNORMAL OPERATION
ANALYSIS and CORRECTION
Four logical steps are required to analyze an operational
problem effectively and make the necessary corrections:
1. Define the problem and its limits.
2. Identify all possible causes.
3. Test each cause until the source of the problem is found.
4. Make the necessary corrections.
The first step in effective problem solving is to define the
limits of the problem. If, for example, the compressor peri-
odically experiences high oil temperatures, do not rely on
this observation alone to help identify the problem. On the
basis of this information, the apparent corrective measure
would appear to be a readjustment of the liquid injection
system. Lowering the equalizing pressure on the thermal
expansion valve would increase the refrigerant feed and the
oil temperature should drop.
If the high oil temperature was the result of high suction
superheat, however, and not just a matter of improper liquid
injection adjustment, increasing the liquid feed could lead
to other problems. Under low load conditions the liquid in-
jection system may have a tendency to overfeed. The high
suction superheat condition, moreover, may only be tempor-
ary. When system conditions return to normal, the unit’s liq-
uid injection will overfeed and oil temperature will drop. In
solving the wrong problem, a new problem was created.
The following list of abnormal system conditions can cause
abnormal operation of the RXB compressor unit:
1. Insufficient or excessive refrigeration load.
2. Excessively high suction pressure.
3. Excessively high suction superheat.
4. Excessively high discharge pressure.
5. Inadequate refrigerant charge or low receiver level.
6. Excessively high or low-temperature coolant to the oil
cooler.
7. Liquid return from the system (carryover).
8. Refrigerant underfeed or overfeed to the evaporators.
9. Blocked tubes in the water-cooled oil cooler from high
mineral content of the water.
10. Insufficient evaporator or condenser sizing.
11. Incorrect refrigerant line sizing.
12. Improper system piping.
13. Problems in electrical service to the compressor unit.
14. Air and moisture present in the system.
Make a list of all deviations from normal plant operation and
normal compressor unit operation. Delete any items which
do not relate to the symptom and separately list those items
that might relate to the symptom. Use the list as a guide to
further investigate the problem.
The second step in problem solving is to decide which items
on the list are possible causes and which items are addi-
tional symptoms. High discharge temperature and high oil
temperature readings may both be symptoms of a problem
and not casually related. High suction superheat or a low
receiver level, however, could cause both symptoms.
The third step is to identify the most likely cause and take
action to correct the problem. If the symptoms are not re-
lieved, move to the next item on the list and repeat the pro-
cedure until you have identified the cause of the problem.
Once the cause has been identified and confirmed, make
the necessary corrections.
MAINTENANCE
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