AGL_Ref_ST_ZO_E_Rev00
29
Condition
Cause
Corrective action
The scroll
compressor does
not run, no buzz
sound can be
heard
Compressor
motor protector
open
Check if there is continuity on the compressor external protector. If the
compressor is warm, it may require considerable time to cool down.
Defective
system control
components
Check if the pressure control or thermostat works properly or if the
controls are open.
Power circuit
open
Check the fuse for a tripped circuit breaker or for an open
disconnected switch.
Burned motor
winding
If motor burned 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 rechecked.
Check for unbalanced voltage.
The scroll
compressor trips
on motor
protection
High discharge
pressure /
suction pressure
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 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 accumulation of debris in the system. For a system with
very short refrigeration lines a suction line accumulator is
recommended.
Compressor
operating
outside the
design limits
Check the compressor suction and discharge pressures while it is
running. Make sure they are within the operating envelope.
Defective motor
protector
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.
