Emerson Copeland Scroll ZR24KRE Application Manuallines page 37

Condition Cause
Excessive Too high
discharge compressor
temperature superheat
Excessive
cooling /
heating load or
inadequate
The scroll
insulation
compressor runs
continuously
Control circuit
inoperative
Oil trap due to
incorrect
piping layout /
sizing
Compressor
lubrication
problem
Oil pump out
due to high
cycling rate
Low gas
velocity
Low ambient
temperature
Low discharge
pressure
Refrigerant
undercharge
System design
load too small
Low suction
Inadequate
pressure
refrigerant
going to the
evaporator
Noise during Anti-reverse
shut-off device
32
Corrective action
Make sure the compressor operates within the acceptable
superheat range published by Emerson.
Check the load design. Make sure that proper insulation is
applied. Correct it as necessary.
Check the thermostat, measure the temperature of the room and
compare with the thermostat; replace or re-calibrate the
thermostat.
Check the LP control switch and replace it if it is found defective.
Check the piping layout design. Installations of pipe being routed
over or around obstacles can inadvertently create unwanted traps
for the oil return. As much as possible the refrigerant line should
travel a direct and straight course between the evaporator and
compressor. It should also be remembered that the entire system
will be coated in oil to some extent. Oil viscosity changes with
temperature. More oil stays in the system than was originally
expected. Make sure the line is correctly sized.
A high cycling rate will pump oil into the system and lead to
lubrication failure. Oil leaves the compressor at start-up and the
short running time is insufficient to return the oil to the compressor
via the suction side. Try to limit the number of cycles to maximum
10 per hour.
System gas velocity changes depending on temperature and load
(capacity control). In low load conditions gas velocity may not be
high enough to return oil to the compressor.
Fit a fan cycling control system.
Check the system for leaks. Observe sight glass for bubbles if
fitted. Add refrigerant until the sight glass is clear.
If no sight glass is fitted, check the evaporator superheat and fill in
with refrigerant.
If the compressor is running in a tandem or in parallel, modulate
the running process.
Lower normal discharge pressure values can lead to insufficient
refrigerant flow to the system.
This can also be verified by checking the evaporator outlet
superheat, if it is found unusually high. Check the selection of the
expansion valve (likely undersized).
This does not have any effect on the durability of the compressor,
no action is necessary.
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