30
AGL_Ref_ST_ZO_E_Rev00
Condition
Cause
Corrective action
Excessive
discharge
temperature
Too high
compressor
superheat
Make sure the compressor operates within the acceptable superheat
range published by Emerson.
The scroll
compressor runs
continuously
Excessive
cooling / heating
load or
inadequate
insulation
Check the load design. Make sure that proper insulation is applied.
Correct as necessary.
Control circuit
inoperative
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.
Compressor
lubrication
problem
Oil trap due to
incorrect piping
layout / sizing
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.
Oil pump out
due to high
cycling rate
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.
Low gas velocity
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.
Low discharge
pressure
Low ambient
temperature
Fit a fan cycling control system.
Refrigerant
undercharge
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.
Low suction
pressure
System design
load too small
If the compressor is running in a tandem or in parallel, modulate the
running process.
Inadequate
refrigerant going
to the
evaporator
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).
Noise during
shut-off
Anti-reverse
device
This does not have any effect on the durability of the compressor, no
action is necessary.
