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How to deal with low pressure faults in air cooled water chiller system?

ClassificationIndustry News 108

How to deal with low pressure faults in air cooled water chiller system?

1. Insufficient or leaking refrigerant. If the refrigerant is insufficient and there is only partial leakage, the balance pressure may be higher during shutdown, while the suction pressure and exhaust pressure may be lower after startup.


The compressor operates with a small current and a short operating time, which means a low voltage fault is reported. The computer displays “LP CURRENT”, and 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 is off.

If most of the refrigerant leaks, the balance pressure is very low, and a low pressure fault is reported when the machine is started. If the suction pressure is lower than 0 “2MPa, the machine cannot be started, the computer displays” LPCURRENT “, and the LP fault indicator light on the unit electronic board is on.”.

Another possibility is that the refrigerant is sufficient, but the expansion valve is too small or blocked (or the refrigerant pipeline is not unblocked), which may also cause a low-pressure fault.

In this situation, the balance pressure is often high, but during operation, the suction pressure is very low, the exhaust pressure is very high, and the operating current of the compressor is also large. At the same time, the valve temperature is also very low, and the expansion valve frosts. After shutdown, the pressure can be restored to balance for a long time.


This situation generally occurs during low temperature operation or at the beginning of each year’s operation, and can be restored to normal after a period of operation.

2. The refrigerant water flow is insufficient, absorbs less heat, and the refrigerant evaporation effect is poor. It is also subcooled and supersaturated steam, which is prone to wet compression. This is manifested by a smaller pressure difference between the inlet and outlet LC -25°C ~ -5°C Low Temperature Chillers, a larger temperature difference, a lower suction temperature, and frost formation at the suction port.

The reasons for insufficient water flow are: there is air or water shortage in the system, and the solution is to install an exhaust valve at a high place in the pipeline for exhaust; If the pipeline filter is blocked or selected too fine, and the water permeability is limited, appropriate filters should be selected and the filter screen should be cleaned regularly;

The selection of water pumps is relatively small and does not match the system. Larger water pumps should be selected or standby water pumps should be used.

3. The evaporator is blocked, the heat exchange is poor, and the refrigerant cannot evaporate. The harm is the same as water shortage. The difference is that the pressure difference between the inlet and outlet water becomes larger, and frost can also occur at the suction port. Therefore, the water chiller should be regularly backwashed.


4. Electrical faults cause false alarms. False alarms caused by moisture, short circuit, poor contact, or damage to the low-voltage protection relay, moisture or damage to the unit electronic board, and communication failures.

5. When the external temperature is low and the cooling water temperature is very low, starting up and running can also cause low pressure faults; During unit operation, low pressure faults may also occur due to insufficient preheating, low refrigerant oil temperature, and insufficient refrigerant separation.

In the former case, measures such as closing the cooling tower and throttling the cooling water can be taken to increase the temperature of the cooling water. In the latter case, the preheating time is extended, and the temperature of the refrigerant oil generally returns to normal after recovering.

6. Ice blockage essentially refers to the presence of water in the system pipeline, and the water in the system moves with the refrigerant to the throttle valve (expansion valve) for throttling expansion, forming a low temperature and low pressure state at the throttle valve outlet.

When the evaporation temperature (outlet temperature of the throttle valve) drops below the freezing point, the moisture in the refrigerant will form ice cubes here, thereby blocking the throttle valve (expansion valve) and forming a low-pressure fault. Ice blockage occurs at the outlet of the throttle valve (expansion valve).

Treatment: It is best to first use a detachable filter, which is filled with “calcium chloride” (a powerful absorbent material) to thoroughly filter the water in the system several times, and then replace it with a disposable filter of the same model.

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