161YORK INTERNATIONAL
FORM 201.18-NM1 (102)
COMPETENT PERSONS TROUBLESHOOTING GUIDE - CONT’D
PROBLEM POSSIBLE CAUSE ACTION POSSIBLE CAUSE ACTION
SYS # HIGH DSCH Poor airflow through condenser coils. Check for airflow restrictions caused by blockages
displayed (High discharge on intake faces of air coils.
pressure trip) Check for damaged fins/return bends.
Check for correct fan operation and direction of
rotation.
Check for non-condensables (air) in system.
Excessive refrigerant charge. Check that the subcooling is correct.
Measured pressure is incorrect. Check discharge transducer calibration and wiring.
SYS # HIGH DSCH TEMP Suction superheat too high. Check suction superheat is within range.
displayed (High discharge Poor airflow through the condenser Check for airflow restrictions caused by blockages
temperature) coils. on intake faces of air coils.
Measured temperature incorrect. Check sensor calibration, location and wiring.
SYS # DSCH LIMITING Discharge pressure unloading due to Check chilled liquid temperature is within range.
displayed (Discharge unit operating above load limit. See Check if ambient air temperature is
pressure unloading) also SYS # HIGH DSCH. above design conditions.
SYS # HIGH OIL PRESS Ball valve in oil circuit closed. Check ball valves are in open position.
DIFF is displayed. (High oil
differential pressure.) Dirty / blocked oil filter. Check and change oil filter cartridge.
SYS # LOW SUCTION Badly adjusted or faulty expansion Check superheat.
displayed valve.
Reduced evaporator performance. Check for restricted chilled liquid flow.
Check for fouled tube surfaces.
Check superheat.
Low refrigerant charge. Check subcooling is correct.
Check for leaks.
Restricted refrigerant flow. Check for blocked filter / drier.
Check YLLSV is operating correctly.
Measured pressure incorrect. Check suction pressure transducer calibration and
wiring.
SYS # LOW CURR/MP/HP Compressor current too low. Check compressor mains supply, fuses, contactors
displayed and wiring. Check mains supply voltage is within
tolerance.
Measured current is incorrect. Check for defective current transformer (resistance
should be between 42 and 44 Ohms.)
Check calibration resistor is correctly fitted.
Compressor motor protector signal Check motor protector and wiring.
failure. Check compressor motor.
Mechanical high pressure cutout Check compressor discharge valve is open.
trip. Check cutout setting and wiring.
No motor cooling. Check motor cooling service valve is open.
Check operation of economizer and motor cooling
TEVs and liquid solenoid valve.
SYS # CURR LIMITING High compressor motor current has Check if liquid temperature is within operating limits.
displayed activated unloading. Check if ambient air temperature is above operating
(Compressor current limits.
unloading.)
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