York MILLENIUM YCAS Series Installation Operation & Maintenance page 152

Troubleshooting
COMPETENT PERSONS TROUBLESHOOTING GUIDE - CONT'D
PROBLEM
SYS # HIGH DSCH
displayed (High discharge
pressure trip)
SYS # HIGH DSCH TEMP
displayed (High discharge
temperature)
SYS # DSCH LIMITING
displayed (Discharge
pressure unloading)
SYS # HIGH OIL PRESS
DIFF is displayed. (High oil
differential pressure.)
SYS # LOW SUCTION
displayed
SYS # LOW CURR/MP/HP
displayed
SYS # CURR LIMITING
displayed
(Compressor current
unloading.)
152
POSSIBLE CAUSE
Poor airflow through condenser coils.
Excessive refrigerant charge.
Measured pressure is incorrect.
Suction superheat too high.
Poor airflow through the condenser
coils.
Measured temperature incorrect.
Discharge pressure unloading due to
unit operating above load limit. See
also SYS # HIGH DSCH.
Ball valve in oil circuit closed.
Dirty / blocked oil filter.
Badly adjusted or faulty expansion
valve.
Reduced evaporator performance.
Low refrigerant charge.
Restricted refrigerant flow.
Measured pressure incorrect.
Compressor current too low.
Measured current is incorrect.
Compressor motor protector signal
failure.
Mechanical high pressure cut-out
trip.
No motor cooling.
High compressor motor current has
activated unloading.
ACTION POSSIBLE CAUSE
Check for airflow restrictions caused by blockages
on intake faces of air coils.
Check for damaged fins/return bends.
Check for correct fan operation and direction of
rotation.
Check for non-condensables (air) in system.
Check that the sub-cooling is correct.
Check discharge transducer calibration and wiring.
Check suction superheat is within range.
Check for airflow restrictions caused by blockages
on intake faces of air coils.
Check sensor calibration, location and wiring.
Check chilled liquid temperature is within range.
Check if ambient air temperature is
above design conditions.
Check ball valves are in open position.
Check and change oil filter cartridge.
Check superheat.
Check for restricted chilled liquid flow.
Check for fouled tube surfaces.
Check superheat.
Check subcooling is correct.
Check for leaks.
Check for blocked filter / drier.
Check YLLSV is operating correctly.
Check suction pressure transducer calibration and
wiring.
Check compressor mains supply, fuses, contactors
and wiring. Check mains supply voltage is within
tolerance.
Check for defective current transformer (resistance
should be between 42 and 44 Ohms.)
Check calibration resistor is correctly fitted.
Check motor protector and wiring.
Check compressor motor.
Check compressor discharge valve is open.
Check cut-out setting and wiring.
Check motor cooling service valve is open.
Check operation of economizer and motor cooling
TEVs and liquid solenoid valve.
Check if liquid temperature is within operating limits.
Check if ambient air temperature is above operating
limits.
ACTION
YORK INTERNATIONAL