Air-cooled modular chiller units are core equipment in commercial central air conditioning and industrial refrigeration systems. They feature dual heating and cooling capabilities, modular design, and stable operation. However, long-term operation is susceptible to malfunctions due to environmental factors, piping issues, electrical control systems, and water quality. This article, based on on-site maintenance experience, categorizes and organizes high-frequency fault phenomena, their core causes, and standardized solutions. It caters to both novice practitioners and professional maintenance needs, and can be directly applied to equipment inspection, routine maintenance, and troubleshooting.
I. Refrigeration system pressure protection failure (high-frequency core failure)
1. Compressor high-pressure protection shutdown
Fault phenomenon : The unit alarms and shuts down. The high voltage value exceeds the equipment's set threshold, and it cannot cool/heat normally. After restarting, it trips again for protection shortly after restarting.
Causes of failure : Dust and oil accumulation on the condenser fins, resulting in a significant decrease in heat dissipation efficiency; insufficient installation space or excessive obstruction of the surrounding area, leading to poor ventilation and heat dissipation; overcharging of refrigerant, causing a surge in condensing pressure; excessively high ambient temperature (high temperatures and direct sunlight in summer); damage to the condenser fan, insufficient speed, or failure to operate.
Solution : After shutting down and disconnecting the power, use a high-pressure water gun with a special cleaning agent to clean the condenser fins, thoroughly removing dust, oil, and debris, and ensuring proper ventilation; clear any obstructions around the unit, leaving adequate space for heat dissipation, and avoid operating in a confined environment; check the system refrigerant pressure, and if there is excess refrigerant, slowly recover the excess refrigerant and calibrate the charging amount; inspect the condenser fan motor, bearings, and capacitor, replace any damaged parts, and ensure the fan operates at full speed; appropriately reduce the unit load during hot weather to avoid continuous full-load operation.
2. Compressor low-pressure protection shutdown
Fault symptoms : The unit alarms low pressure, frequently starts and stops, has extremely poor cooling effect, and in severe cases, it stops completely and cannot be restarted. The low pressure is far below the standard operating value.
Causes of failure : Refrigerant leakage or insufficient refrigerant in the system; blockage of the dryer filter or expansion valve, causing throttling in the pipeline and insufficient liquid supply; expansion valve opening too small, resulting in insufficient liquid supply for evaporation; insufficient chilled water flow, scale buildup and blockage of the evaporator, reducing heat exchange efficiency; long-term low-load operation of the unit and excessively low ambient temperature.
Solution : Conduct a comprehensive leak inspection of the refrigeration pipes, joints, and valves; locate the leak point and repair it by welding; perform vacuuming; and add refrigerant of the matching type according to standards. Disassemble, clean, or replace the clogged dryer filter and clear impurities from the pipes. Professionally adjust the expansion valve opening and calibrate the liquid supply. Clean scale and impurities from the evaporator pipes, check the water pump operation status, and ensure that the water flow meets the standards. Adjust the unit's operating parameters appropriately in low-temperature environments to avoid false low-pressure protection.
3. Compressor overload protection
Fault symptoms : The compressor operating current exceeds the standard, the thermal protector trips, the unit stops, and it still cannot operate normally after restarting. This often occurs under high temperature and high load conditions.
Causes of failure : Unstable power supply voltage, phase loss, poor circuit contact; compressor operating under overload for a long time, excessive heat load; aging compressor coil, worn bearings, mechanical jamming; abnormal system pressure (high pressure, low pressure) leading to high operating resistance; poor heat dissipation leading to excessively high machine body temperature.
Solution : Check the three-phase power supply voltage, current, and terminals; tighten loose wiring; troubleshoot phase loss and voltage deviation issues; repair power supply faults; reduce the unit's operating load to avoid continuous full-load operation of multiple modules; disconnect the power to check the compressor's insulation resistance and mechanical operating status; replace aged or severely worn compressor parts; replace the compressor directly if the fault is severe; troubleshoot and repair pre-existing faults such as abnormal high and low pressure and poor heat dissipation; restart operation only after the compressor body has completely cooled down.
II. Unit Start-up, Shutdown, and Operational Abnormalities
1. The compressor cannot start.
Fault symptom : The unit is powered on normally and there are no error messages on the control panel, but the compressor does not start or stops immediately after starting.
Causes of failure : main power supply or control power supply failure; blown fuse or tripped circuit breaker; damaged contactor or relay; open circuit in control circuit; compressor overload; high/low pressure protection lockout not reset; temperature sensor failure; abnormal signal causing the main board to be unable to start; compressor body burnt out or stuck.
Solution : Inspect the power supply lines, switches, and fuses of the entire unit, replace damaged parts, and restore normal power supply; use a multimeter to test the continuity of the control circuit, contactors, and relays, repair circuit faults, and replace damaged electrical control components; manually reset various pressure protection and overload protection devices, investigate and resolve the root cause of protection triggering; calibrate the inlet and outlet water temperature and ambient temperature sensors, and replace sensors with distorted or damaged signals; check the compressor's operating condition and replace it promptly if the compressor itself is damaged.
2. Frequent start-ups and shutdowns of the generating unit
Fault phenomenon : The unit starts up and then stops after a few seconds to several minutes, then restarts automatically after a short time, repeating this cycle repeatedly and unable to operate stably.
Causes of failure : Insufficient or excessive refrigerant, causing severe fluctuations in system pressure; unstable water flow, with fluctuating flow rates, triggering water flow protection; unreasonable temperature control parameter settings, with an excessively small temperature difference threshold; interference with electrical control signals and sensor data drift; large fluctuations in mains voltage.
Solution : Accurately calibrate the refrigerant charge amount and troubleshoot pipeline pressure fluctuations; overhaul the water pump, clean the water filter, and fully open pipeline valves to stabilize water flow; reset the unit's temperature control parameters and adjust the start-stop temperature difference appropriately; replace the inaccurate temperature sensor, tidy up the electrical control circuit, and reduce signal interference; install a voltage stabilizer to stabilize the power supply voltage.
III. Abnormal water temperature and heat exchange efficiency
1. The outlet water temperature is too high and the cooling effect is poor in cooling mode.
Fault phenomenon : The unit operates normally without alarms, but the chilled water cools down slowly, the indoor cooling effect is poor, and the outlet water temperature is much higher than the set value.
Causes of failure : Poor condenser heat dissipation, resulting in reduced cooling efficiency; insufficient refrigerant or minor leakage; scale buildup on the evaporator, blockage of heat exchange surfaces, leading to low heat exchange efficiency; insufficient water pump flow, or valves not fully open in the pipeline; terminal heat load exceeding the unit's rated cooling capacity.
Solution : Deep clean the condenser fins and optimize unit ventilation and heat dissipation; check for leaks and add refrigerant to ensure sufficient refrigerant in the system; regularly chemically clean the evaporator pipes for scale and sludge; overhaul the water pump, clean impurities from the pipes, and fully open the water circulation valves; adjust the number of operating modules according to the actual load, and add units or reduce the terminal load in overload scenarios.
2. In heating mode, the outlet water temperature is low and the temperature rises slowly.
Fault phenomenon : The unit operates normally under heating conditions, but the hot water temperature cannot reach the set standard, resulting in poor indoor heating effect.
Causes of failure : Poor defrosting of the unit in low-temperature winter environments, resulting in frost, ice, and blockage of the fins; insufficient refrigerant, leading to decreased heating cycle efficiency; leakage or incomplete reversal of the four-way valve, causing failure of heating operation; abnormal outdoor fan speed, resulting in heat dissipation and heat exchange imbalance; and deviation of the water temperature sensor signal, causing abnormal main control adjustment.
Solution : Initiate the unit's forced defrosting program, manually clean the frost on the fins, check the defrosting sensor and heating components, and repair defrosting faults; check for leaks and add refrigerant to ensure normal heating cycle pressure; check the four-way valve's condition, repair any issues such as gas leakage or reversing blockage, and replace it directly if damaged; inspect the outdoor fan motor and capacitor to ensure normal fan operation; calibrate or replace the water temperature sensor and correct the main control adjustment parameters.
IV. Water system malfunction
1. Water flow switch protection alarm
Fault phenomenon : The unit displays a water flow fault, triggering protection shutdown and indicating insufficient water flow.
Causes of failure : Circulating water pump failure, motor damage, impeller blockage and wear; water filter blockage, obstructing water circulation in the pipeline; water valve not fully open, pipeline blockage; water flow switch failure, signal malfunction; system water shortage, air entering the pipeline.
Solution : Inspect the water pump, clean impurities from the impeller, and repair or replace the faulty water pump; shut down the system, disassemble and clean the water filter screen, and regularly drain and remove impurities; check all water valves to ensure they are fully open, and unclog blocked pipes; test the on/off state and signal of the water flow switch, and calibrate or replace damaged switches; replenish water and vent air from the water system to eliminate air blockages in the pipes.
2. Scale buildup in water pipes and blockages in pipes
Fault symptoms : Water flow rate decreases year by year, heat exchange efficiency continues to decline, unit energy consumption increases, and high and low pressure and water flow protection are easily triggered.
Causes of the malfunction : The circulating water was not softened, resulting in high water hardness; long-term lack of sewage discharge and cleaning led to the accumulation of scale, silt, and rust; and aging and corrosion of the pipes caused impurities to fall off and block the pipes.
Solution : Install water softening and purification equipment to improve the quality of circulating water; regularly perform chemical descaling and high-pressure flushing on evaporators and water pipes; conduct monthly water system drainage to remove impurities; replace aging and corroded pipes to ensure smooth water circulation.
V. Electrical control and communication failures
1. Communication failure between the main unit and the wired controller.
Fault symptoms : The wired controller reports an error, the unit cannot be controlled, parameters are not refreshed, the unit's automatic operation is uncontrollable, and common communication fault codes include F6.
Causes of failure : Reversed, loose, or broken communication AB lines; excessively long communication lines, poor shielding, or signal interference; damage to the wired controller or mainboard communication chip; inconsistent operating modes of the main and auxiliary modules of the modular unit.
Solution : Power off and check the communication line, correct the wiring sequence of AB lines, tighten the terminals, and reconnect the broken line; shorten the communication line distance, replace the shielded communication line, and keep it away from high-voltage equipment to reduce interference; test the communication module between the wired controller and the motherboard, and replace the damaged chip or accessory; unify the main and auxiliary module operating modes, and recalibrate by powering on.
2. Controller parameters lost, program malfunction.
Fault symptoms : The unit's operating parameters are disordered, the modes are incorrect, it frequently reports errors and shuts down, and it cannot switch between cooling and heating modes normally.
Causes of failure : Unstable power supply to the motherboard, frequent power outages; malfunctioning controller program, lost parameters; depleted motherboard battery, storage failure.
Solutions : Stabilize the power supply to the equipment to avoid frequent power outages and tripping; recalibrate the unit's operating parameters and restore the factory standard configuration; replace the motherboard's spare battery and rewrite the equipment parameters; if the program is severely corrupted, flash the firmware and restart to repair the system fault.
VI. Winter-specific problem: Poor defrosting
Fault phenomenon : During winter heating, the outdoor fins of the unit are severely frosted and iced, and automatic defrosting is not possible, resulting in a significant decrease in heating capacity and even shutdown of the entire unit.
Causes of failure : The defrost sensor is malfunctioning and cannot accurately detect the frosting temperature; the defrost heating element or defrost circuit is faulty; the four-way valve is delayed in reversing or is stuck; the outdoor fan is faulty, and insufficient airflow leads to frost accumulation; low temperature and high humidity environment exacerbates frost formation; and the unit's defrosting program parameters are unreasonable.
Solution : Inspect and replace the faulty defrost sensor, and calibrate the detection accuracy; repair the defrost heating component, fix the circuit fault, and replace damaged parts; adjust the four-way valve reversing function to ensure smooth switching between heating and defrosting modes; repair the outdoor fan to ensure that the air volume meets the standard; optimize the unit's defrost start and stop parameters, and manually force defrosting when necessary, and clean the fins of ice.
VII. Key Points for Daily Operation and Maintenance Prevention
1. Quarterly maintenance: Clean the condenser, evaporator fins and water filter, check refrigerant pressure and pipe sealing, and tighten electrical control terminals.
2. Annual maintenance: Descaling and rust removal of the entire machine, testing the compressor insulation and operating current, calibrating various sensor parameters, and checking the wear and tear of the four-way valve, water pump, and fan.
3. Seasonal maintenance: In summer, focus on checking heat dissipation and high-voltage protection conditions; in winter, focus on checking the defrosting system, pipeline antifreeze, and voltage stability.
4. Water quality control: Use softened water for long-term use, regularly discharge sewage and remove impurities to prevent scale and impurities from clogging pipes and heat exchange equipment.
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