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What Problems Can Be Caused By Low Pressure Failure of Chillers?

Jan. 19, 2024

1. Increased energy consumption

If the compressor is running at low pressure, the motor load will become smaller, and a chiller with a low-pressure failure will waste electricity under the same cooling conditions.

2. Smaller cooling capacity

If the chiller suction pressure is low and the return air volume is reduced, the cooling capacity will not reach the target.


What are the causes of low chiller pressure? How to solve?

1. Insufficient refrigerant or leakage

Insufficient refrigerant will lead to system pressure failure, resulting in lower suction pressure. The chiller will issue a low pressure alarm and the unit will stop.

Solution: The refrigerant leakage part can be diagnosed from the piping connection of compressor, condenser, filter, expansion valve, evaporator and other accessories. After troubleshooting, charging the right amount of refrigerant can solve the problem.

Water Cooled Screw Chiller

 Water Cooled Screw Chiller


2. Low ambient temperature

When the outside temperature is low, the temperature of cooling water and compressor oil will also be low. If the chiller is started at this time, a low pressure fault alarm will be issued.

Solution: If the cooling water temperature is too low, close the cooling tower fan or throttle the cooling water to raise the cooling water temperature. If the compressor oil temperature is too low, extend the chiller preheating time, the refrigeration oil temperature will return to normal.


3. System pipe blockage

When the chiller is installed, it is inevitable that impurities will penetrate into the system, and after using it for a long time, various impurities will also enter the system. When there are too many impurities, the filter will be blocked, so that the refrigerant channel and return air will be reduced, and low pressure failure will occur.

Solution: Clean the filter, condenser and evaporator.

4. Expansion valve opening is too small or damaged

Expansion valve is the throttling device of refrigeration system. Too little expansion valve opening will allow less refrigerant vapor to pass through. Too little refrigerant vapor will make the compressor inlet pressure is too low, resulting in low pressure failure.

Solution: Increase the expansion valve opening appropriately or replace the damaged expansion valve.

5. Relay failure, electrical system false alarm

Relays play the role of indirect protection devices, compressor normal suction pressure is generally 0.4 ~ 0. 6MPa, when the suction pressure is lower than 0. 2MPa, will lead to low pressure protection relay action, the chiller stopped running. Sometimes the low-pressure relay will not work properly due to moisture, circuit breakage and other faults.

Solution: Check the low pressure relay and repair or replace it. Non-technical personnel can contact the manufacturer for help to solve the problem.

Air Cooled Screw Chiller

 Air Cooled Screw Chiller


By design, most chillers achieve maximum tonnage at the lowest kW usage by operating at approximately 70-75% of load and the lowest entering condensate temperature (ECWT). Understanding chiller efficiency and the impact of load and ECWT will help facilities determine the most efficient chiller configuration to maximize energy cost savings.

The first step in maximizing chiller efficiency is to establish a method to record chiller operating data in a daily log. It is common for facilities to maintain chiller logs. Collecting and trending chiller operation data can be done automatically. Chiller performance at full and partial loads can be accurately measured, efficiency calculated and the cause of inefficiencies diagnosed.

Once the state of the chiller is determined (baseline), operational changes can be made to improve efficiency and measure the results. They are subject to wear, tear and aging. The best advice is not to assume anything until proven by accurate, ongoing verification.


The best way to provide accurate data, obtain specific results and minimize problems is to verify the flow to the chiller for tonnage measurements and other calculations to determine efficiency. Flow meters can be of the high quality turbine type, magnetometer (in-line) or ultrasonic (external) and provide the most accurate gallons per minute (GPM) flow readings. gpm can be determined by using a pressure gauge or the delta pressure of the chronograph. Delta temperature does not actually measure the GPM flow rate, but it can identify proper flow rates and flow-related problems.


It can also be affected by other conditions not directly related to flow, such as fouled cooler barrels, non-condensing gas and refrigerant levels, which make interpretation more difficult. However, using delta temperature along with a flow meter or delta pressure gauge creates a powerful diagnostic tool that can identify problems affecting chiller system efficiency.


Along with proper flow rates, check and calibrate temperature sensors/gauges, pressure sensors/gauges, meters, etc., periodically or as problems are identified.

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