Emerson Copeland Scroll ZR24KRE Application Manuallines page 36

Condition Cause
Compressor
motor
protector open
Defective
system control
The scroll components
compressor does
Power circuit
not run, no buzz
open
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
AGL_AC_ST_ZRKRE_E_Rev01
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 pressure control or thermostat works properly or if the
controls are open.
Check the fuse for a tripped circuit breaker or for an open
disconnected switch.
If motor is burned due to undersized contactors, the contacts will
be 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 the contactor
manufacturer data sheet. If the application of the compressor is
changed the contactor sizing should be rechecked.
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 is likely in case of
excessive pressure drop in the liquid line or too much 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 an 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.
31