Common faults and causes of screw chillers Jan 12, 2022
Common faults and causes of screw chillers
1. High voltage fault

The compressor discharge pressure is too high, causing the high pressure protection relay to act. The compressor discharge pressure reflects the condensing pressure. If the pressure is too high for a long time, it will cause the compressor running current to be too large, which will easily burn the motor, and also easily cause damage to the valve plate of the compressor discharge port. The reasons for the high pressure fault are as follows:

1)The cooling water temperature is too high and the condensation effect is poor. The cooling water required by the screw chiller is rated at 30~35°C. The high water temperature and poor heat dissipation will inevitably lead to high condensing pressure. This phenomenon often occurs in high temperature seasons. The reasons for the high water temperature may be: cooling tower failure, such as the fan is not turned on or even reversed, the water distributor does not rotate, the cooling water temperature is very high, and it rises rapidly; the outside temperature is high, the water circuit is short, and the amount of water that can be circulated In this case, the cooling water temperature is generally maintained at a high level, which can be solved by adding a water storage tank.
2)The cooling water flow is insufficient and cannot reach the rated water flow. The main performance is that the pressure difference between the inlet and outlet water of the water cooling unit becomes smaller (compared with the pressure difference at the beginning of the system operation), and the temperature difference becomes larger. The reason for insufficient water flow is the lack of water or the presence of air in the system. The solution is to install an exhaust valve at the height of the pipeline for exhausting; the pipeline filter is blocked or too thin, and the water permeability is limited. Clean the filter screen regularly; the water pump is small and not matched with the system.

3)Excessive refrigerant charge. This situation generally occurs after maintenance, and it is manifested as high suction and exhaust pressure, balance pressure, and high compressor operating current. It should be deflated according to the suction and discharge pressure and balance pressure and operating current under rated operating conditions until it is normal.

screw chillers

2. Low voltage fault
The suction pressure of the compressor is too low, causing the low pressure protection relay to act. The compressor suction pressure reflects the evaporative pressure. If the suction pressure is low, the amount of return air will be small, and the cooling capacity will be insufficient, resulting in a waste of electric energy. For the compressor motor with return air cooling, the heat dissipation is poor, and the motor is easily damaged! The solution is the same as the high pressure fault, try to keep the compressor in the normal pressure range. The reasons for the failure are as follows:
1)Insufficient or leaking refrigerant. If the refrigerant is insufficient or partially leaked, the equilibrium pressure may be high when the machine is shut down, and the suction pressure and discharge pressure are low after the machine is turned on, the compressor running current is small, and the operating time is short, and a low-pressure fault is reported.
2)Evaporator is clogged and heat exchange is poor. Refrigerant cannot evaporate, and its harm is the same as that of water shortage. The difference is that the pressure difference between inlet and outlet becomes larger, and frost will form on the suction port. Therefore, the screw chiller should be backwashed regularly.
3)The outside temperature is low. When the cooling water temperature is very low, a low pressure fault will also occur when the unit is running, due to insufficient preheating, the temperature of the refrigerating oil is low, and the refrigerant is not sufficiently separated, and a low pressure fault will also occur. For the former case, measures such as closing the cooling tower and throttling the cooling water can be taken to increase the cooling water temperature. In the latter case, the preheating time is extended, and the temperature of the refrigeration oil can generally return to normal after the temperature rises.

water cooling unit
3. compressor overheating failure
The thermistor is embedded in the compressor motor winding, and the resistance is generally 1kΩ. When the winding is overheated, the resistance value will increase rapidly, the thermal protection module will act to cut off the operation of the unit, and at the same time, the overheating fault will be displayed, and the fault indicator will be on. The causes of compressor overheating failure are as follows:
1)The compressor is overloaded and runs over current. The possible reasons are: the cooling water temperature is too high, the refrigerant is charged too much, or there is air and other non-condensable gases in the refrigeration system, resulting in a large compressor load, which is manifested as overcurrent and accompanied by high-voltage faults.
2)Compressor overcurrent operation due to electrical fault. If the three-phase power supply voltage is too low or the three-phase unbalance, the current or a certain phase current is too large; the AC contactor is damaged, the contacts are ablated, causing the contact current to be too large or the current is too large due to phase loss.

water cooled condensing units

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