Common Issues in Chiller Operation and Solutions

During the operation of the chiller, there will always be wear and tear. Therefore, we need to regularly record and analyze its operating parameters, listen to the sounds during operation, check the usage of refrigerant and refrigeration oil, and perform regular maintenance operations. The following lists the common problems during the operation of the chiller and their solutions, hoping to be helpful to everyone.

A technician specializing in industrial refrigeration, commercial central air - conditioners, and industrial dehumidification equipment analyzed the reasons for the too - small temperature difference between the inlet and outlet water of the chiller.
The technician said that when users encounter such a situation with the chiller: they are using a chiller, the current inlet water temperature is 24°C, the outlet water temperature is 23°C, and the temperature difference is too small to meet the user's needs. The main reasons for the too - small temperature difference between the inlet and outlet water are as follows:

Noise is an annoying sound, and continuous noise can also pollute the surrounding environment. The common reasons for the noise generated by the chiller fan are as follows:
When the blades rotate, they will rub against or impact the air. The noise frequency is composed of multiple frequencies, all of which are related to the rotation speed of the fan.
Suggestion: If the axial - flow fan has a configuration of moving blades and static blades, the number of blades of the two is preferably different to avoid greater noise resonance.
When the blades generate eddies, noise will also be produced. During the operation of the fan, eddies will be generated on the back of the moving blades. This eddy not only reduces the efficiency of the fan but also generates noise. To reduce this phenomenon, the installation angle of the blades should not be too large, and the curvature of the fan blades should be smooth, without sudden large changes.
Resonance with the air duct shell generates noise. The inner - surface joints of the air duct and the fan shell should be flat to avoid roughness and tearing sounds. In addition, in the design, sometimes sound - proof materials can be covered outside the air duct to reduce noise.
In addition to the fixed noise of the fan itself, there are many other noise sources. For example, abnormal noise may be caused by insufficient precision of the bearings, improper assembly, or poor maintenance. The motor part can also generate noise. Some are caused by poor design or manufacturing quality control, but sometimes it is caused by the internal and external cooling fans of the motor. Therefore, when selecting equipment, it is necessary to strictly screen regular products and consider factors such as the human - centered design of the equipment.

The computer controller controls each module through the communication line and the main interface board. The main reasons for communication failure are poor contact or disconnection of the communication line, especially poor contact caused by the interface being damp and oxidized. In addition, faults of the unit electronic board or the main interface board, improper selection of the address dip - switch, and power failure can all cause communication failure.

The suction pressure of the compressor is too low, causing the low - pressure protection relay to act. The suction pressure of the compressor reflects the evaporation pressure, and the normal value should be between 0.4 - 0.6MPa, and the protection value is set at 0.2MPa. If the suction pressure is low, the return air volume is small, the cooling capacity is insufficient, resulting in a waste of electrical energy. For compressors cooled by return air, the motor heat dissipation is poor, and the motor is easily damaged.
The reasons for the low - pressure fault are as follows:
(1) Insufficient refrigerant or leakage. If the refrigerant is insufficient and only partially leaked, the balance pressure may be relatively high when the machine is stopped, and the suction pressure is low and the discharge pressure is also low after startup. The operating current of the compressor is small, and the low - pressure fault is reported after a short running time. The computer displays "LP CURRENT", and at the same time, the LP fault indicator light on the unit electronic board is on. After a few seconds, the computer displays "LP RESET", and the LP fault indicator light on the unit electronic board goes off. If most of the refrigerant leaks, the balance pressure is very low, and the low - pressure fault is reported as soon as the machine is started. If the pressure on the suction side is lower than 0.2MPa, the machine cannot be started, the computer displays "LP CURRENT", and the LP fault indicator light on the unit electronic board is on. There is also a possibility that the refrigerant is sufficient, but the opening degree of the expansion valve is too small or blocked (or the refrigerant pipeline is not unobstructed), which may also cause a low - pressure fault. In this case, the balance pressure is often high, but the suction pressure is very low during operation, the discharge pressure is very high, the operating current of the compressor is also very large, and at the same time, the valve temperature is very low, and the expansion valve is frosted. The pressure takes a long time to return to balance after the machine is stopped. This situation generally occurs during low - temperature operation or at the beginning of each year's operation, and it can return to normal after running for a period of time.
(2) Insufficient chilled water flow, less heat absorption, poor refrigerant evaporation effect, and it is super - cooled and supersaturated steam, which is likely to cause wet compression. It is manifested as a decrease in the pressure difference between the inlet and outlet water of the unit, an increase in the temperature difference, a low suction temperature, and frost formation at the suction port. The reasons for the insufficient water flow are: air in the system or water shortage. The solution is to install an exhaust valve at the high point of the pipeline for exhaust; the pipeline filter is blocked or the selected one is too fine, and the water - passing capacity is limited. A suitable filter should be selected and the filter screen should be cleaned regularly; the selected water pump is too small and not matched with the system. A larger water pump should be selected, or the standby water pump should be started.
(3) The evaporator is blocked, and the heat exchange is poor, so the refrigerant cannot evaporate. Its harm is the same as water shortage. The difference is that it is manifested as an increase in the pressure difference between the inlet and outlet water, and frost may also appear at the suction port. Therefore, the unit should be back - flushed regularly.
(4) False alarm caused by electrical faults. Due to the low - pressure protection relay being damp and short - circuited, poor contact, or damaged, the unit electronic board being damp or damaged, and communication faults causing false alarms.
(5) When the outside air temperature is low and the cooling water temperature is very low, starting the machine will also cause a low - pressure fault; when the unit is running, due to insufficient pre - heating, the temperature of the refrigeration oil is low, and the refrigerant is not fully separated, which will also cause a low - pressure fault. For the former situation, measures such as closing the cooling tower and throttling the cooling water can be taken to increase the cooling water temperature. For the latter situation, extend the pre - heating time, and it can generally return to normal after the temperature of the refrigeration oil rises.

The discharge pressure of the compressor is too high, causing the high - pressure protection relay to act. The discharge pressure of the compressor reflects the condensing pressure, and the normal value should be between 1.4 - 1.6MPa, and the protection value is set at 2.0MPa. If the pressure is too high for a long time, it will cause the operating current of the compressor to be too large, easily burn the motor, and also easily damage the valve plate at the discharge port of the compressor.
The reasons for the high - pressure fault are as follows:
(1) The cooling water temperature is on the high side, and the condensing effect is poor. The rated working condition of the cooling water required by the chiller unit is 30 - 35°C. High water temperature and poor heat dissipation will inevitably lead to high condensing pressure. This phenomenon often occurs in the high - temperature season. The reasons for the high water temperature may be: cooling tower failure, such as the fan not running or even reversing, the water distributor not rotating, manifested as a very high cooling water temperature that rises rapidly; high outside air temperature, short water circuit, and less recyclable water volume. In this case, the cooling water temperature generally remains at a relatively high level, and the solution is to increase the storage water tank.
(2) Insufficient cooling water flow, not reaching the rated water flow. The main manifestation is that the pressure difference between the inlet and outlet water of the unit becomes smaller (compared with the pressure difference at the beginning of the system's operation), and the temperature difference becomes larger. The reasons for the insufficient water flow are system water shortage or air in the system. The solution is to install an exhaust valve at the high point of the pipeline for exhaust; the pipeline filter is blocked or the selected one is too fine, and the water - passing capacity is limited. A suitable filter should be selected and the filter screen should be cleaned regularly; the selected water pump is too small and not matched with the system.
(3) The condenser is scaled or blocked. The cooling water is generally tap water, and it is easy to scale above 30°C. And because the cooling tower is open - type and directly exposed to the air, dust and foreign objects can easily enter the cooling water system, causing the condenser to be dirty and blocked, reducing the heat - exchange area, lowering the efficiency, and also affecting the water flow. It is manifested as an increase in the pressure difference and temperature difference between the inlet and outlet water of the unit. Touching the condenser, the temperature is very high up and down, and the liquid - outlet copper pipe of the condenser is scalding. The unit should be back - flushed regularly, and chemical descaling should be carried out if necessary.
(4) Excessive refrigerant charging. This situation generally occurs after maintenance, manifested as high suction and discharge pressures, high balance pressure, and high operating current of the compressor. Under the rated working condition, bleed according to the suction and discharge pressures, balance pressure, and operating current until normal.
(5) The refrigerant is mixed with non - condensable gases such as air and nitrogen. This situation generally occurs after maintenance when the evacuation is not thorough. It can only be drained, evacuated again, and re - charged with refrigerant.
(6) False alarm caused by electrical faults. Due to the high - pressure protection relay being damp, poor contact, or damaged, the unit electronic board being damp or damaged, and communication faults causing false alarms. For this false fault, often the HP fault indicator light on the electronic board is not on or is dimly lit. The manual reset of the high - pressure protection relay is invalid. The computer displays "HP RESET", or it disappears automatically. The measured operating current of the compressor is normal, and the suction and discharge pressures are also normal.

A thermistor is embedded in the winding of the compressor motor, with a resistance value of generally 1kΩ. When the winding overheats, the resistance value will increase rapidly. When it exceeds 141kΩ, the thermal protection module SSM acts, cuts off the unit operation, and at the same time displays the overheating fault, and the TH fault indicator light is on.
The reasons for the compressor overheating fault are as follows:
(1) The compressor load is too large, running with over - current. The possible reasons are: too high cooling water temperature, excessive refrigerant charging, or non - condensable gases such as air in the refrigeration system, resulting in a large compressor load, manifested as over - current and accompanied by a high - pressure fault.
(2) Electrical faults cause the compressor to run with over - current. For example, the three - phase power supply voltage is too low or unbalanced, resulting in an excessive current or excessive current in one phase; the AC contactor is damaged, and the contacts are burned, causing excessive contact current or excessive current due to phase - loss.
(3) The thermal protection module SSM is damp or damaged, the intermediate relay is damaged, and the contacts are poor, manifested as an overheating fault occurring as soon as the machine is started, and the compressor cannot be started. If the unit electronic board fails or there is a communication fault, it may also falsely report the overheating fault.

The temperature at the outlet of the expansion valve reflects the evaporation temperature, which is a factor affecting heat exchange. Generally, the temperature difference between it and the chilled water outlet temperature is 5 - 6°C. When the low - valve - temperature fault occurs, the compressor will stop. When the valve temperature rises, it will automatically resume operation, and the protection value is ~2°C.
The reasons for the low - valve - temperature fault are as follows:
(1) A small amount of refrigerant leakage, generally manifested as a low - valve - temperature fault rather than a low - pressure fault. When the refrigerant is insufficient, it evaporates at the outlet of the expansion valve, causing a temperature drop, manifested as frost formation at the outlet of the expansion valve, a relatively high temperature at the suction port (superheated steam), a decrease in cooling capacity, and slow cooling.

(2) The expansion valve is blocked or the opening degree is too small. The system is not clean, such as the refrigerant pipeline not being cleaned thoroughly after maintenance, the refrigerant being impure or containing moisture.
(3) Insufficient chilled water flow or the evaporator is blocked, resulting in poor heat exchange, a low evaporation temperature, and a low suction temperature. The opening degree of the expansion valve is adjusted according to the suction temperature. A low temperature leads to a small opening degree, thus causing a low - valve - temperature fault.
(4) False alarm caused by electrical faults, such as poor contact of the valve temperature wire, resulting in the computer displaying ~5°C without change.