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Screw refrigeration compressors are volume-type compressors that compress gas by means of changes in volume. The compressor operates by having two screws with spiral grooves inside the casing rotate while meshing with each other; together with the interaction between these screws and the inner walls of the casing as well as the inner walls of the suction and discharge ports, this mechanism causes changes in the volume between the teeth, thereby enabling the absorption, compression, and discharge of gas. Features of screw refrigeration compressors: simple structure, few components, and high strength and wear resistance of rotor bearings, etc ； Forced air supply, meaning that the exhaust volume is hardly affected by the exhaust pressure ； It can maintain high efficiency over a wide range of operating conditions ； Sliding valve regulation is employed, enabling stepless energy adjustment and insensitivity to the incoming fluid. Screw refrigeration compressors are now widely used in freezing and refrigeration as well as HVAC systems. This article summarizes the common faults and their causes, in the hope of being helpful to you. I. Excessive exhaust pressure 1. Excessively high inlet temperature of the condenser or insufficient flow rate ； 2. There is air or non-condensable gases in the system ； 3. Severe scaling inside the copper tubes of the condenser ； 4. Excessive refrigerant charge ； 5. The intake valve on the condenser is not fully open ； 6. Inhale pressure is higher than normal ； 7. Pump failure. II. Excessive low exhaust pressure 1. Excessive water flow rate through the condenser ； 2. The inlet water temperature of the condenser is too low ； 3. A large amount of liquid refrigerant enters the compressor ； 4. Insufficient refrigerant charge ； 5. The inhalation pressure is below the standard. III. Excessively high suction pressure 1. Excessive refrigerant charge ； 2. At full load, a large amount of liquid refrigerant flows into the compressor ； IV. Insufficient suction pressure 1. The refrigerant liquid outlet valve of the condenser is not fully opened ； 2. The refrigerant filter is clogged ； 3. Improper adjustment or malfunction of the expansion valve ； 4. Insufficient refrigerant charge ； 5. Excess lubricating oil circulates in the refrigeration system ； 6. The water inlet temperature of the evaporator is too low ； 7. Insufficient water flow through the evaporator. V. Compressor stops due to high-pressure protection 1. Insufficient water flow through the condenser ； 2. Clogged copper tubes in the condenser ； 3. Excessive refrigerant charging ； 4. The high-voltage protection setting is incorrect. 6. The compressor stops operating due to overload of the main motor. 1. Excessively high or low voltage, as well as imbalance between phases ； 2. Excessive exhaust pressure ； 3. The return water temperature is too high ； 4. Overload or original component failure ； 5. Short circuit in the main motor or terminal block. VII. Compressor stops operating due to main motor temperature protection 1. Excessively high or low voltage ； 2. Excessive exhaust pressure ； 3. The return temperature of cold water is too high ； 4. Insufficient refrigerant charge ； 5. Fault in the temperature protection device ； 6. The gas inlet valve of the condenser is closed. VIII. Compressor stops due to low-pressure protection 1. Refrigerant filter clogged ； 2. Expansion valve failure ； 3. Insufficient refrigerant charge ； 4. The liquid outlet valve of the condenser is not opened. IX. The compressor will not operate: 1. The overload protection has been disengaged or the fuse in the control circuit has blown ； 2. Poor contact in the control circuit ； 3. The compressor relay coil is burned out ； 4. Phase error. X. The unloading system does not work. 1. Faulty thermostat ； 2. Failure to unload the solenoid valve ； 3. The unloading mechanism is damaged. XI. High starting load or failure to start 1. Excessively high exhaust pressure ； 2. Exhaust check valve leakage ； 3. The energy adjustment is not at zero ； 4. Excessive oil or liquid accumulation inside the machine ； 5. Some mechanical wear ； 6. The pressure relay is faulty or the set pressure is too low. XII. Continuous vibration after the unit is started 1. Tighten the unit’s foundation bolts ； 2. Misalignment and eccentricity of the compressor and motor axes ； 3. Unbalanced compressor rotor ； 4. Resonance occurs due to the same vibration frequency between the unit and the pipes ； 5. Poor balance of the coupling. 13. Vibration shortly after the unit starts up and then stabilization: 1. Excessive lubricating oil or liquid being drawn in ； 2. Liquid slugging occurs due to oil accumulation in the compressor. 14. Abnormal noises during operation 1. Foreign objects inside the rotor ； 2. Thrust bearing wear and rupture ； 3. Wear of sliding bearings, wear of the rotor and casing ； 4. Loose operating connectors (couplings, etc.) ； 5. Oil pump cavitation. 15. The compressor shuts down automatically without reason 1. The high-pressure relay activates ； 2. Oil temperature relay activates ； 3. Fine filter pressure difference relay activates ； 4. Control circuit failure ； 5. Overload. 16. Insufficient cooling capacity 1. Insufficient oil injection volume ； 2. The spool is not in the correct position ； 3. Excessive inhalation resistance ； 4. Excessive wear gap in the machine ； 5. Fault in the energy regulation device. 17. The energy regulation mechanism does not function or is malfunctioning. 1. The four-way valve fails to work; there is a fault in the control circuit ； 2. The oil pipeline or connector is blocked ； 3. Excessive clearance in the oil piston ； 4. The slide valve or oil piston is stuck ； 5. Low oil pressure. 18. Excessively high exhaust temperature or oil temperature. 1. Excessive compression ratio ； 2. The oil cooler has poor heat transfer efficiency ； 3. Inhaling superheated gas ； 4. Insufficient fuel injection volume. 19. High temperature of the compressor casing 1. Heat generation in the frictional parts of the casing ； 2. Overheated inhaled gas ； 3. Excessively high compression ratio ； 4. The oil cooler has poor heat transfer efficiency. 20. High fuel consumption: 1. Excessive oil during a single oil separation process ； 2. The secondary oil separator has oil return. 21. Low oil pressure 1. Improper adjustment of the oil pressure control valve ； 2. Excessive fuel injection ； 3. Excessive or insufficient oil level ； 4. Internal oil leakage ； 5. Rotor wear, reduced oil pump efficiency ； 6. Blocked oil circuit (clogged fine filter) ； 7. Insufficient oil quantity or poor oil quality. 22. Rising oil level 1. Refrigerant dissolved in oil ； 2. Enter the liquid refrigerant. 23. The compressor keeps reversing when shut down (a few reversals are normal). 1. The suction check valve is stuck and fails to close ； 2. The spring of the inhalation check valve lacks sufficient elasticity.