Flooded type water cooled screw chiller (PCB Control)
104
VIII.
Troubleshooting
1.
Protection items
Midea screw chiller has many protection measures and devices. There
’re many features to aid in
troubleshooting. By using the alarm information, DI/O, AI/O and operating conditions of the chiller during
chiller operation, it
’s convenient to find the possible problem. Verify that the chiller is properly configured,
including options and/or accessories.
Protection items:
Protection
Purpose
High pressure / low pressure
protection of compressor
Ensures the compressor runs in normal range and
ensures its work life.
Converse phase, lack of phase
protection
Protects the compressor from damage because of
converse phase or lack of phase of power.
Anti-freezing protection during
refrigeration
Protects the key components such as evaporator,
condenser and water pipe etc. from damage because of
the expanse caused by the water becomes into ice
Overload protection
Protects the compressor from burn due to overload
running.
Over current protection of compressor
Protects the compressor from burn due to over current
running under bad conditions.
Internal protection
Makes the compressor run safely under permitted
conditions.
Anti-overheating protection of system
Protects the compressor from burn because of running
lack of refrigerant or lubricating oil.
Water flow switch protection
Protects the compressor and the water pump motor from
burn because there is lack of cooling water or chilled
water.
Protection of sensor fault
Ensures the data from sensor is correct to prevent the
system from wrong action.
Oil level and oil pressure difference
protection
Ensures the compressor to run normally.
High discharge temperature protection
Makes the compressor run safely under permitted
conditions.
Phase reversal/phase loss (phase protection)
Power supply A/B/C should exist simultaneously and differ from each other by 120° phase angle. If
not, Phase reversal or phase loss fault will occur and be displayed on screen. Before unit start when
Phase reversal or phase loss fault occurs, the chiller won
’t start; when Phase reversal or phase loss
fault occurs during chiller operating, the chiller will stop according to protective stop program. Both
compressors are shut down and water pumps and cooling tower fan stops in accordance with
normal shutdown procedure. When fault record gets cleared and both temperature and time
condition gets satisfied, the chiller can restart.
Water flow failure (both chilled water and cooling water)
PCB controller begins to detect chilled/cooling water flow switch after water pumps get energized
180s. The switch will disconnect if water flow less than set point and water flow loss signal will
generate if it lasts for 5s. During chiller operation (including dual heads unit), any flow switch
disconnects for 5s continuously, Unit stops according to protective stop program.
