Viii.troubleshooting; Protection Items - Midea LSBLG MCF Series Technical & Service Manual

MCAC-CTSM-2018-1

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
High pressure / low pressure
protection of compressor
Converse phase, lack of phase
protection
Anti-freezing protection during
refrigeration
Overload protection
Over current protection on the compressor
Internal protection
Anti-overheating protection of the system
Water flow switch protection
Protection of the sensor fault
Oil level and oil pressure difference protection
High discharge temperature protection

Phase reversal/phase loss (phase protection)
Power supply A/B/C should exist simultaneously and differ from each other by a 120° phase angle.
If not, Phase reversal or phase loss fault will occur and be displayed on screen. Before the unit
starts when phase reversal or phase loss fault occurs, the chiller won't start; when Phase reversal or
phase loss fault occurs during chiller operations, the chiller will stop according to the protective stop
program. Both compressors are shut down and water pumps and cooling tower fans stop in
accordance with normal shutdown procedures. When the fault record is cleared and both
temperature and time conditions are satisfied, the chiller can restart.

Water flow failure (both chilled water and cooling water)
PCB controller begins to detect chilled/cooling a water flow switch after the water pumps get
energized 180s. The switch will disconnect if water flow is less than a set point and the water flow
loss signal will occur if it lasts for more than 5s. During chiller operations (including dual heads unit),
any flow switch that disconnects for 5s continuously, Unit stops according to protective stop
program.
Flooded type water cooled screw chiller (MIC)
Purpose
Ensures the compressor runs in a normal range and
guarantees its service life.
Protects the compressor from damage because of a
converse phase or lack of phase of power.
Protects key components such as the evaporator,
condenser and water pipe from damage because of
the expansion caused by water freeing into ice
Protects the compressor from burning due to overload
running.
Protects the compressor from burning due to over
current running under bad conditions.
Enables the compressor to run safely under permitted
conditions.
Protects the compressor from burning because of
running a lack of refrigerant or lubricating oil.
Protects the compressor and the water pump motor
from burning because there is lack of cooling water or
chilled water.
Ensures the data from the sensor is correct to prevent
the system from wrong action.
Ensures the compressor can run normally.
Enables the compressor to run safely under permitted
conditions.
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