Emerson Copeland YHV029RG Application Manuallines page 44

Condition Cause
Compressor
motor protector
open
Defective system
control
components
The scroll
Power circuit
compressor does
open
not run, no buzz
sound can be heard
Burned motor
winding
High discharge
pressure /
suction
pressure
The scroll
compressor trips
on motor
protection
Compressor
operating
outside the
design limits
Defective motor
protector
Excessive Too high
discharge compressor
temperature superheat
Excessive
cooling /
heating load or
The scroll
inadequate
compressor runs
insulation
continuously
Control circuit
inoperative
AGL_HP_VS_YHV_RG_RT_EN_Rev00
Corrective action
Check if there is continuity on the compressor external protector. If the
compressor is warm, it may require considerable time to cool down.
Check if the system controls and its components like pressure
switches and sensors are working properly or if they are in alarm state.
Fix the reason for the alarm.
Check the fuse for a tripped circuit breaker or for an open
disconnected switch.
If motor burn is due to undersized contactors, this is observed when
the contacts welded together. Complete motor burnout on all three
phases despite the presence of a functioning protection system can be
the result. For sizing information please consult with contactor
manufacturer data sheet. If the application of the compressor is
changed the contactor sizing should be checked again.
Check for unbalanced voltage.
For high discharge pressure:
Check for system leaks. With system leaks at the low-pressure
side, air as non-condensable gas could enter the system and
create high pressure.
Check the system design. Make sure the discharge line is correctly
sized: undersized discharge line can increase discharge pressure.
This is also true for an undersized condenser. Correct the
component selection as needed.
Check the fan motor, make sure it is running properly in the right
direction. Check the condenser: if dirt has been accumulated it will
clog the airflow; clean as necessary. High discharge pressure is
also caused by an overcharged system and high ambient
temperature surrounding the condenser.
For high suction pressure, check the "evaporator superheat" first to
diagnose the problem:
High superheat at the evaporator outlet: this is likely in case of
excessive pressure drop in the liquid line or too m uch vertical lift on
the pipework.
Low superheat at the evaporator outlet is usually the consequence
of oversized selection of the expansion valve or incorrect bulb
sensor mounting. The valve may freeze up in the open position due
to accumulation of debris in the system. For a system with very
short refrigeration lines a suction line accumulator is
recommended.
Check the compressor suction and discharge pressures while it is
running. Make sure they are within the operating envelope.
If all operating conditions are normal, the voltage supply at the
compressor terminals is balanced and within limits, the compressor
crankcase temperature is within normal limits, and the amperage
drawn is within the specified range, the motor protector may be
defective.
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 controls, measure the temperature and pressure and
compare with the controls; replace or re-calibrate the controls.
Check the LP control switch and replace it if it is found defective.
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