Avoid Downtime, Cut Costs: Smart Maintenance for Smarter Chillers

 Screw water-cooled chillers typically operate around 3,000 hours per year, depending on China's climate and geographical conditions. Regular and scientific maintenance is crucial to ensure long-term, reliable operation, extend the lifespan, and reduce operating costs.

Maintenance and Upkeep
Preventive maintenance during operation and inspection involves creating annual and monthly maintenance plans based on actual operating conditions.

Shutdown Procedures
In winter, clean and dry the unit. Open the drain valve to empty the shell-and-tube heat exchanger to avoid freezing. The shutdown sequence is: chiller off - cooling tower fan off - cooling water pump off - chilled water pump off. Special attention to anti-freezing:

1. Drain the evaporator and condenser if the unit is outdoors below 0°C during standby.
2. Interlock the water flow switch with the unit to prevent freezing when the chilled water flow switch malfunctions.
3. Ensure water in the evaporator is flowing or completely drained when charging or discharging refrigerant.

Concentration %	Freezing temperature (℃)	Concentration %	Freezing temperature (℃)	Concentration %	Freezing temperature (℃)
4.6	-2	19.8	-10	35	-21
8.4	-4	23.6	-13	38.8	-26
12.2	-5	27.4	-15	42.6	-29
16	-7	31.2	-17	46.4	-33

The concentration of ethylene glycol is a mass concentration.

Startup Procedures
After a long shutdown, prepare by thoroughly checking and cleaning the Screw refrigeration unit, cleaning the water pipeline system, inspecting the pump, tightening wiring connections, and preheating the compressor. The startup sequence is: cooling tower fan on - cooling water pump on - chilled water pump on - chiller on.

Common Fault Analysis and Troubleshooting

Fault	Possible Causes	Detection and Troubleshooting Methods
Excessive discharge pressure	Air or non-condensable gases in the system	Bleed gases via the refrigerant port and re-evacuate if needed
	Cooling tower fan malfunction	Inspect and repair the fan to restore operation
	Excessive suction pressure	See "Excessive suction pressure"
	High ambient temperature
	Insufficient cooling water flow	Check the cooling water system and increase the water flow.
	Low compressor oil level	Check the oil level through the sight glass and add refrigeration oil
Low discharge pressure	Low suction pressure	See "Low suction pressure"
	Refrigerant leakage or insufficient charge	Detect leaks and recharge refrigerant
	Cooling water temperature too low	Check if the cooling tower capacity is excessively large or if the ambient temperature is too low
Excessive suction pressure	Discharge pressure too high	See "Discharge pressure too high"
	Excessive refrigerant charge	Release part of the refrigerant
	Liquid refrigerant flowing from the evaporator into the compressor
	Chilled water inlet temperature exceeds maximum allowable value	Check and adjust the expansion valve, ensuring its temperature-sensing bulb is in tight contact with the suction pipe and fully insulated from the outside
Low suction pressure	Clogged filter drier	Replace the filter drier cartridge
	Expansion valve improperly adjusted or malfunctioning	Adjust to the appropriate superheat temperature, or check if the expansion valve's temperature-sensing bulb is leaking
	Insufficient refrigerant in the system	Detect leaks and recharge refrigerant
	Chilled water inlet temperature significantly lower than specified value
	Insufficient chilled water flow	Check if the pressure in the evaporator's inlet and outlet pipelines is too low, and adjust the chilled water flow rate
Compressor shutdown due to high-pressure protection	Cooling water temperature too high
	Cooling tower fan malfunction	Overhaul the cooling tower fan
	Incorrect high-pressure shutdown setting	Check the high-pressure switch
Compressor shutdown due to motor overload	Voltage too high or too low	Check that the voltage does not exceed or fall below the rated voltage by ±10%
	Discharge pressure too high	Refer to "Discharge pressure too high"
	Cooling water temperature too high	Check if the cooling tower capacity is too small
	Overload component malfunction	Check the compressor current and compare it with the rated full-load current specified on the compressor
	Motor or terminal short circuit	Check the corresponding resistance of the motor and terminals
Compressor shutdown due to built-in temperature protection switch activation	Voltage too high or too low	Check the voltage; it must not exceed the specified range mentioned above
	Discharge pressure too high	See "Discharge pressure too high"
	Chilled water inlet temperature too high
	Compressor built-in temperature protection switch failure	Replace the component
	Insufficient refrigerant in the system	Check for fluorine leakage
The compressor shuts down due to low-pressure protection	Drier filter blockage	Replace the drier filter element
	Expansion valve failure	Adjust or replace the expansion valve
	Incorrect low-pressure shutdown setting	Check the low-pressure switch
	Insufficient refrigerant	Recharge the refrigerant
Loud compressor noise	Insufficient compressor refrigerating oil	Check the oil level in the sight glass and add refrigerating oil
The compressor fails to start	Overcurrent relay trips and fuse burns out	Replace the damaged components
	Control circuit not connected	Check the wiring of the control system
	No current	Check the power supply
	High-pressure protection or low-pressure protection	See the section on suction and discharge pressure faults above
	Contactor coil burned out	Replace the damaged component
	Incorrect power phase sequence connection	Reconnect and swap any two wires
	Water system failure, water flow switch open circuit	Check the water system
	The operation display shows an alarm signal	Check the alarm type and take corresponding measures
	Incorrect setting of start-stop time	Check and reset the settings
	Temperature sensor detects temperature exceeding set value	Check and reset