Fault analysis of refrigerator operating conditions

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1. The suction pressure or evaporation pressure is too low: As the temperature of the warehouse or the refrigerant decreases, the suction pressure also decreases, which is a normal phenomenon. To determine whether the suction pressure is too low, one must first consult the thermodynamic property table using the suction pressure to find the corresponding evaporation temperature.  The evaporation temperature should be 4–6°C lower than the refrigerant carrier outlet temperature, and 8–12°C lower than the warehouse temperature in cases where the refrigerant evaporates directly. If these temperature differences are exceeded, it indicates that the suction pressure is too low.     If the suction pressure is too low, the cooling capacity of the compressor will be significantly reduced.  Note: When consulting tables of thermodynamic properties, the gauge pressure shown on the pressure gauge should be converted to absolute pressure. Absolute pressure = Gauge pressure + 0.1 MPa. 1.1 Insufficient refrigerant supply to the evaporator. 1.1.1 Causes: 1) Insufficient refrigerant in the system; 2) Clogged liquid filter; 3) The refrigerant supply solenoid valve is not open or is malfunctioning; 4) The opening degree of the supply valve is too small. All of the above situations are accompanied by an increase in suction superheat.  1.1.2 Exhaust method: It should be exhausted sequentially from the condenser, receiver to the throttle valve.  1) Add refrigerant to the specified amount. 2) Perform cleaning or replacement. 3) The supply solenoid valve is not open; it needs to be opened. If the supply solenoid valve is malfunctioning, it must be replaced. 4) Make appropriate adjustments. For Freon-based systems, attention should also be paid to whether there is ice blockage in the thermal expansion device and whether the superheat setting is too high. Thereafter, adjust the opening degree of the throttle valve as appropriate. To reduce the liquid supply volume and increase the superheat, turn the superheat knob of the thermal expansion valve clockwise; to increase the liquid supply volume and decrease the superheat, turn it counterclockwise. Each time the throttle valve is adjusted, observe the changes in suction pressure and suction temperature for about 30 minutes, until the desired operating parameters are achieved.  1.2 Leakage from the lead screw gasket of the dry evaporator
1.2.1 Causes: Damage or displacement of the lead screw gasket in the dry evaporator can result in leakage. In such cases, a portion of the refrigerant bypasses the evaporator and flows directly into the suction pipe; consequently, the amount of refrigerant actually entering the evaporator for heat exchange decreases. This situation is often accompanied by a drop in suction temperature and even liquid entrainment in the suction stream.  1.2.2 Elimination method: The supply valve should be closed, the refrigerant in the evaporator recovered to the condenser or receiver, and the end cover removed to replace the guide gasket.  1.3 Poor heat transfer on the refrigerant side inside the evaporator 1.3.1 Reasons: If the refrigerant contains a high level of oil, as it evaporates in the evaporator, the oil separates out and adheres to the surface of the heat exchange tubes, thereby affecting heat exchange.  1.3.2 Elimination methods: The oil consumption of the compressor should be minimized as much as possible, and the accumulated oil in the condenser, receiver, and evaporator should be removed promptly. Select a lubricant with an appropriate solidification temperature based on the operating temperature.  1.4 Poor heat transfer on the refrigerant side of the evaporator
1.4.1 Causes: Rust, scale formation, or ice buildup on the refrigerant side of the evaporator, as well as frost formation on the refrigerant pipes and air coolers, can all adversely affect the heat exchanger’s heat transfer efficiency, resulting in a decrease in the evaporation temperature.  1.4.2 Elimination methods: The coolant system should have its water circuits cleaned regularly, and the heat exchangers and air coolers should have their frost removed promptly. Therefore, a coolant solution with an appropriate concentration should be selected based on the operating temperature. Saltwater solutions are corrosive, and anti-corrosion measures should be taken.  1.5 Excessive resistance loss in the suction piping
1.5.1 Causes: The non-return suction stop valve does not open fully, or the valve core is stuck or dislodged; the suction filter is dirty or clogged with ice.  1.5.2 Elimination method: The check-type suction stop valve is not fully open; it needs to be opened ； If the valve core of the check-type suction stop valve gets stuck or falls off, it needs to be repaired or replaced ； If the intake filter is dirty or clogged with ice, it needs to be cleaned or repaired.  2 Excessive exhaust pressure or condensation pressure: As the ambient temperature or the temperature of the cooling water rises, the exhaust pressure increases as well, which is a normal phenomenon. To determine whether the exhaust pressure is too high, one must first consult a thermodynamic property table using the exhaust pressure to find the corresponding condensation temperature.  In ammonia systems, the condensation temperature of water-cooled condensers should be 4–6°C higher than the outlet temperature of the cooling water; for evaporative condensers, it should be 5–10°C higher than the local wet-bulb temperature℃ ； In ammonia systems, the condensation temperature of horizontal and modular condensers should be 7°C higher than the average outlet temperature of the cooling water. For air-cooled condensers, the condensation temperature is generally 10–15°C higher than the inlet air temperature, while for evaporative condensers, it is 10–15°C higher than the local wet-bulb temperature. If these temperature differences are exceeded, it indicates that the exhaust pressure is too high.  If the exhaust pressure is too high, the power consumption of the compressor will **increase**.  Note: When consulting tables of thermodynamic properties, the gauge pressure shown on the pressure gauge should be converted to absolute pressure. Absolute pressure = Gauge pressure + 0.1 MPa 2.1 High cooling water temperature or insufficient water volume 2.1.1 Cause: The inlet temperature of the cooling water in the refrigeration system should be below 32℃ ； Leakage in the gasket of the condenser end cover, which reduces the amount of water that actually enters the condenser, can also lead to excessively high condensation pressure.  2.1.2 Exclusion method: For vertical condensers, the temperature difference between the inlet and outlet water of the cooling water should be controlled at 2–3°C, while for horizontal condensers, this difference should be maintained at 4–6°C; therefore, it is necessary to control both the temperature of the cooling water and its flow rate ； Replace the condenser end cover gasket.  2.2 Scaling on the water side of the condenser 2.2.1 Causes: Due to the high temperatures in the condenser, the water side provides an environment suitable for the growth of certain microorganisms as well as the formation of scale, which leads to a reduction in heat exchange efficiency.  2.2.2 Removal methods: Scale should be removed in a timely manner, or disinfectants should be used to kill bacteria.  Note: Chemical agents and hard-bristled brushes can be used to clean scale; the use of wire brushes is strictly prohibited, especially in copper tube heat exchangers.  2.3 Excessive refrigerant accumulation in the condenser 2.3.1 Causes: During normal operation of the unit, the liquid outlet valve of the condenser should be fully open. In systems without a liquid storage tank, if too much refrigerant is present in the system, this can lead to an excessively high liquid level in the condenser, which in turn covers part of the condensation tubes and reduces the condensation area, resulting in a higher condensation temperature.  2.3.2 Exclusion method: The height of the liquid in the condenser can be determined by touch. Release a proper amount of refrigerant.  2.4 Excessive oil accumulation in the condenser 2.4.1 Reason: If an ammonia unit consumes a large amount of oil, and there is still a significant amount of lubricating oil in the exhaust gases, this oil will condense outside the condensation tubes, forming an oil film that hinders heat exchange.  2.4.2 Elimination methods: The fuel consumption of the unit should be reduced as much as possible, and the oil accumulated in the condenser should be drained promptly.  2.5 Non-condensable gases in the condenser
2.5.1 Causes: Incomplete vacuum pumping of the system, excessive air getting mixed in during the charging of refrigerant, and in systems where the suction pressure is below zero; air may leak from flange joints and valves. Air mainly accumulates in the upper part of the condenser, occupying some of the condensation area and raising the condensation pressure; therefore, the air should be removed promptly.  2.5.2 Exhaust method: Ammonia refrigeration systems must be exhausted through an air separator. If Freon is used without an air separator, the compressor should be shut down while the cooling water continues to circulate. After 20 minutes, open the condenser vent valve by a quarter turn to release air; this should be done until water droplets appear at the base of the valve.  2.6 High air humidity 2.6.1 Reasons: Evaporative condensers rely primarily on the evaporation of water to remove heat; if the air humidity is too high, water does not evaporate easily, the heat exchange efficiency decreases, and the condensation pressure rises ； Water-cooled condensers also experience increased condensation pressure due to high air humidity, which reduces the cooling efficiency of the cooling tower and raises the temperature of the cooling water.  2.6.2 Emission methods: The former should reduce the heat load, while the latter should increase the circulation rate of cooling water or reduce the heat load.  2.7 Excessive resistance in the exhaust pipeline 2.7.1 Cause: Any loss of resistance in the refrigeration system is harmful. The exhaust resistance of the compressor mainly arises from the oil separation filter element in the oil separator, the check-type exhaust shut-off valve, as well as the elbows and valves in the exhaust piping.  2.7.2 Troubleshooting method: Inspection should be carried out sequentially from the oil separator filter to the condenser; all pipeline valves must be fully opened.  Note: The difference between the exhaust pressure and the condensation pressure should not exceed 0.1 MPa; if it does, it must be replaced.  3. Excessively high fuel injection temperature. The oil temperature of the unit should be maintained between 40 and 65°C; if WL series special lubricant is used, the oil temperature can be kept between 40 and 70°C. Either too high or too low a temperature can affect the proper operation of the compressor.  3.1 Excessively high cooling water temperature or insufficient water volume. The oil outlet temperature of a water-cooled oil cooler is 8–10°C higher than the cooling water outlet temperature; see 2.1 for details.  3.2 Scaling on the condensate side: See 2.2 for details.  3.3 Excessively high condensation pressure (temperature). The oil outlet temperature of a thermosyphon oil cooler is generally 10–20°C higher than the condensation temperature; it is necessary to find ways to reduce the exhaust pressure, thereby lowering the condensation temperature and the oil temperature. For details, see section 2.  3.4 There is a relatively large amount of oil on the refrigerant side of thermal siphon oil coolers. 3.4.1 Reason: If lubricating oil is present in the refrigerant, it will accumulate as the refrigerant evaporates, thereby affecting heat exchange.  3.4.2 Exclusion method: The oil accumulated on the refrigerant side in the thermal siphon oil cooler should be drained promptly. The ammonia system should promptly drain the oil stored in the thermal siphon receiver, to prevent excessive lubricating oil from entering the thermal siphon oil cooler along with the refrigerant.  3.5 Insufficient liquid spray volume 3.5.1 Causes: In a liquid spray cooling system, an insufficient amount of liquid spray, a clogged liquid spray filter, an unopened or malfunctioning liquid spray solenoid valve, or an excessively small opening degree of the high-temperature thermal expansion valve can all lead to excessive oil temperature ； Since the liquid spray volume is determined by the difference between the exhaust pressure and the intermediate pressure, and the intermediate pressure is related to the evaporation pressure, excessively high evaporation pressure and excessively low exhaust pressure can also result in insufficient liquid spray volume.  3.5.2 Exclusion methods: The former should be excluded one by one, starting from the condenser, liquid storage tank, and up to the high-temperature thermal expansion valve for liquid injection ； The latter should reduce the evaporation pressure and increase the exhaust pressure to ensure a sufficient pressure difference for the liquid spray volume.  Note: The interval for removing scale and oil residue from the oil cooler is 3-6 months.  4. Compressor operation with liquid carryover: When liquid is carried over into the compressor’s suction side, it causes the lubricating oil to emulsify. This reduces its lubrication and sealing effectiveness, and may also lead to wear of moving parts. Such situations should be avoided as much as possible.  For compressors with a flooded evaporator structure, the suction superheat should be controlled within 0.5–1°C; for those with a dry evaporator structure, it should be maintained at 5–15°C. If the superheat is too low, there is a risk of liquid entering the suction line. The main phenomena that occur when liquid is drawn in during inhalation include: a decrease in inhalation temperature, frosting or an increase in the area affected by frosting on the machine body and the inhalation end fittings, abnormal vibrations and noise from the compressor, and a decrease in exhaust temperature.  4.1 Excessively high liquid level in the ammonia liquid separator or low-pressure circulation reservoir 4.1.1 Remedial measures: The ammonia liquid separator should not contain any residual liquid, and the liquid level in the low-pressure circulation reservoir should be maintained between one-third and one-half of the tank’s height during operation. If the liquid level is too high, the level controller and the supply solenoid valve should be checked.  4.2 Excessive liquid supply to the evaporator 4.2.1 Causes: Excessive opening of the throttle valve, or too low a superheat setting for the thermal expansion valve, resulting in an excessive amount of refrigerant being supplied and liquid entering the suction side.  4.2.2 Exclusion method: The opening degree of the throttle valve or the superheat of the thermal expansion valve should be adjusted appropriately.  4.3 Leakage of the lead gasket on the end cover of the dry evaporator; see 1.2 for details. 4.4 Poor heat transfer efficiency of the evaporator: In low-temperature brine chillers and ethanol chillers that use thermal expansion valves to control the supply of refrigerant, the presence of oil on the refrigerant side or scale or ice formation on the water side reduces the heat transfer efficiency of the evaporator, resulting in a decrease in the amount of liquid that evaporates. As for thermal expansion valves, they can only adjust the amount of refrigerant supplied within a certain range; this leads to an increasing amount of liquid refrigerant inside the evaporator, eventually causing liquid to be carried in the suction gas.  4.5 Excessive resistance in the suction line 4.5.1 Cause: Excessive resistance in the suction line leads to a reduction in the amount of refrigerant drawn in by the compressor, which in turn results in an increase in the amount of liquid refrigerant inside the evaporator, eventually causing liquid to be carried in with the suction gas.  4.5.2 Exclusion method: Mainly check whether the intake filter is dirty or clogged with ice. When liquid entrainment occurs in the suction line of the compressor, the non-return suction shut-off valve should be immediately throttled down and the load reduced; thereafter, the liquid supply valve should be closed.  5 Excessive oil pressure difference: For screw compressors, the oil pressure must be at least 0.18 MPa higher than the discharge pressure; otherwise, the compressor will trigger an alarm and shut down. This issue is primarily manifested as excessively low oil pressure.  5.1 Low oil level in the oil reservoir 5.1.1 Cause: The oil level is too low, resulting in a reduced amount of circulating oil and unstable oil pressure.  5.1.2 Troubleshooting method: Oil should be returned or added in a timely manner.  5.2 The oil circuit system, the coarse oil filter, or the fine oil filter elements are overly clogged. 5.2.1 Cause: Excessive debris in the oil circuit system, the coarse oil filter, or the fine oil filter elements leads to increased resistance, reduced flow of oil, and lower oil pressure.  5.2.2 Elimination method: Cleaning should be performed.  Note: It is recommended to remove and clean the coarse and fine oil filters after 72 hours of operation for newly installed units; after doing this three times, the filters should be cleaned every three months of operation.  5.3 Excessively high oil temperature 5.3.1 Causes: As the oil temperature rises, the viscosity of the lubricating oil decreases, its fluidity increases, and the amount of fuel injected into the engine increases, which leads to a drop in oil pressure.  5.3.2 Elimination method: Worn components should be repaired. Components with out-of-tolerance gaps should be replaced.  Note: This situation should be inspected by a professional.  6. Increased oil consumption of the compressor: The increased oil consumption is mainly reflected in the decrease in the oil level within the oil separator.  6.1 Increased fuel injection volume 6.1.1 Causes: High oil temperature, as well as wear and tear of internal compressor components and excessive clearance, can all lead to an increase in fuel injection volume.  6.1.2 Troubleshooting method: Adjust the oil temperature to an appropriate value, and inspect or replace worn components.  6.2 Liquid entrainment in the compressor suction line
6.2.1 Causes: When liquid gets entrained in the compressor suction line, part of the liquid fails to evaporate and enters the oil separator along with the exhaust gas. This causes the discharge temperature of the unit to drop, leading to rapid “oil flooding” in the unit.  6.2.2 Elimination method: The check-type suction stop valve should be closed promptly and the load reduced, while adjusting the liquid supply to the evaporator and economizer.  6.3 High exhaust temperature 6.3.1 Cause: As the exhaust temperature rises, the amount of oil vapor increases; the oil separator is unable to separate this oil vapor, resulting in increased fuel consumption. The discharge temperature of screw compressors is generally <90°C. 6.3.2 Remedy: Note that excessively high discharge temperatures can cause the lubricating oil to degrade, leading to the formation of sludge, gum, and deposits. This prevents the compressor from being properly lubricated. Therefore, it is necessary to control both the oil temperature and the discharge temperature of the compressor.  6.4 Low exhaust temperature 6.4.1 Cause: When the exhaust temperature is low, the lubricating oil droplets contained in the gas cannot be effectively separated. As a result, excessive amounts of lubricating oil leave the oil separator along with the exhaust gas, leading to an increase in oil consumption.  6.4.2 Elimination method: Control the exhaust temperature.  6.5 Poor oil separation effect 6.5.1 Causes: If the oil filter element in the oil separator becomes loose, or if the sealing gasket is damaged or displaced, leading to gas bypass, the oil separation effect will be reduced. Furthermore, if the oil separation filter element is heavily contaminated, the air flow velocity increases, causing the adsorbed oil to be easily blown away by the gas, thereby reducing its oil-separating efficiency. If the resistance is too high, there is also a possibility that the oil separator filter may break. The pressure difference before and after the oil separation filter element generally should not exceed 0.06 MPa.  6.5.2 Troubleshooting method: Inspect or replace the filter element.  6.6 Excessive oil in the third-stage oil separator or poor oil return 6.6.1 Causes: An excessively high oil level in the third-stage oil separator may submerge the oil filter element, and the oil may be blown away by the exhaust gas ； At the same time, the effective gas separation space decreases, resulting in a reduced oil separation efficiency.  6.6.2 Exclusion method: Check the oil level in the tertiary oil sight glass. Under normal conditions, this oil chamber is not supposed to contain oil; if oil is present, open the return valve to send the oil back to the compressor’s suction side.  Note: The internal cleaning period for the oil separator is two years.  7 Excessive starting load, failure to start, or immediate shutdown after starting 7.1 The slide valve does not settle at the zero position; starting under load 7.1.1 Cause: When starting under load, the starting load is high, making it difficult to start.  7.1.2 Exclusion method: Move the four-way directional valve to the load-reduction position; the pointer should return to zero.  7.2 The machine is filled with lubricating oil or a large amount of liquid refrigerant. 7.2.1 Causes: Liquid accumulates in the suction line and flows into the compressor, or the oil pump remains active for too long; as a result, a large amount of liquid remains inside the machine, and since liquid cannot be compressed, this makes starting difficult.  7.2.2 Exclusion method: Rotate the coupling several times to drain the liquid, wait until it feels loose, and then start the compressor.  7.3 Severe wear of moving parts leads to increased friction. 7.3.1 Causes: This is manifested as an increase in current and sticking of the turning gear oil. The main causes are bearing breakage or wear, as well as the entry of foreign objects that cause wear to the rotor.  7.3.2 Exclusion method: Maintenance must be carried out.  7.4 Excessive deviation in the coaxial alignment between the compressor and the motor 7.4.1 Cause: An excessive deviation in the coaxial alignment between the compressor and the motor leads to increased torque, higher starting load, and difficulty in starting.  7.4.2 Elimination method: Re-adjust the coaxiality is required.  7.5 The power circuit breaker is not closed or the emergency stop switch on the cabinet has not been turned off. 7.5.1 Resolution method: Resolve the current-related issue, supply power in accordance with the product requirements, and release the emergency stop switch.  7.6 The differential pressure controller or relay fails to reset after being disconnected. 7.6.1 Cause: The unit shut down automatically due to protection measures, and the differential pressure controller or relay did not reset, resulting in an inability to start the unit. (The high-pressure protection of the compressor and motor overload require manual reset.)  7.6.2 Elimination method: Identify the cause of the fault and eliminate it, then reset manually, or wait for automatic reset before turning the device on.  7.7 Improper adjustment of the pressure controller or temperature sensor results in the contacts remaining open. 7.7.1 Solution: When the contacts of the pressure controller or temperature sensor remain open, the unit activates its parameter protection mechanism; it is necessary to conduct inspections as required and replace the relevant components.  7.8 Improper adjustment or malfunction of the temperature controller 7.8.1 Troubleshooting method: Adjust the setting value of the temperature controller or replace it.  7.9 Burnout of contactor and intermediate relay coils, poor contact of contacts, or faults in the control circuit. 7.9.1 Troubleshooting method: Recheck the relevant electronic components and circuits.  7.10 Burned or open motor windings 7.10.1 Troubleshooting method: If the motor windings are burned or open, the motor will not start, and it is necessary to perform maintenance on the motor.  8 Automatic shutdown of the compressor during operation 8.1 Relays or programs that trigger automatic protection 8.1.1 Reasons: During operation, the relevant parameters reach the set values for the compressor’s automatic protection, or these set values are incorrect; as a result, the relay or controller program activates and the compressor shuts down automatically.  8.1.2 Troubleshooting method: Investigations should be carried out based on the items related to the protection action; the cause of the fault must be identified and resolved before the system can be restarted.  Warning: It is strictly prohibited to restart the device by changing the protection setting values.  8.2 Relay protection activation in the main power circuit 8.2.1 Cause: Internal wear of the compressor or motor, along with an excessive heat load on the evaporator, leads to an elevated operating current; as a result, the thermal relay in the main circuit activates and the compressor stops, with an overload error indicated for the motor.  8.2.2 Elimination method: First, turn the shaft by hand to check for mechanical faults; if turning it by hand is too difficult, seek professional assistance for repairs ； If the heat load is too high, as indicated by high intake pressure, the heat load should be reduced or the system should be operated at a reduced load after it is restarted.  8.3 Loose control circuits 8.3.1 Cause: Due to vibrations or other factors affecting the unit’s control box, the wiring terminals may become loose, leading to incorrect shutdowns.  8.3.2 Elimination method: The corresponding wiring should be inspected and tightened.  8.4 Control component failures 8.4.1 Causes: Due to the long operating time of the unit, relays and heat exchangers may develop errors, causing the indicated values to deviate from the protection setpoints and resulting in incorrect commands that lead to automatic shutdown.  8.4.2 Exclusion method: Relays and heat exchangers should be calibrated at least once a year. In addition, large voltage fluctuations and lightning strikes can very likely cause fuses and electronic components to burn out, and the damaged parts need to be replaced.  Excessive vibration in unit 9. 9.1 Low suction pressure. 9.1.1 Cause: When the suction chamber of the screw compressor is at a high vacuum level, the compressor will experience abnormal vibrations or noise.  9.1.2 Elimination methods: At this time, check whether the supply volume is appropriate for the compressor load; also verify that all check valves on the suction side are open and that the suction filter is not clogged.  9.2 Ingestion of excessive refrigerant liquid 9.2.1 Cause: An excessive supply of liquid to the evaporator allows a large amount of liquid to enter the machine; since liquid cannot be compressed, this causes the compressor to vibrate abnormally.  9.2.2 Exclusion method: The liquid supply volume should be reduced.  9.3 Excessive deviation in the coaxiality between the compressor and the motor 9.3.1 Causes: An excessive deviation in the coaxiality between the compressor and the motor, as well as improper installation of the coupling, can not only lead to unstable machine operation and increased noise, but also cause abnormal damage to the rotor, bearings, and shaft seals.  9.3.2 Elimination method: Re-adjust the coaxiality is required.  9.4 Vibration of the unit caused by system pipelines 9.4.1 Causes: 1) If the suction and exhaust pipelines are too long, after the unit has been operating for some time, the welded pipelines may undergo stress deformation due to stress release, which leads to vibration of the unit or the pipelines.  2) If the natural vibration frequency of the unit is similar to that of the system piping, resonance will occur, which also leads to excessive vibrations.  9.4.2 Exclusion methods: 1) Support fixation must be added or the pipeline must be cut and reconnected.  2) It is necessary to change the location of the system pipeline support points.  9.5 The corner bolts of the unit, main engine, and motor are not tightened. 9.5.1 Reason: Loose corner bolts of the unit, main engine, and motor can cause vibration in the unit.  9.5.2 Elimination method: Tighten the bolts.  9.6 Poor quality of the unit’s installation foundation 9.6.1 Cause: Vibration or settlement of the installation foundation can lead to vibration in the unit.  9.6.2 Elimination method: The depth of foundation construction should be appropriately increased according to the geological conditions of the area of use.  10 Abnormal noises occur when the compressor is running 10.1 Foreign objects inside the compressor 10.1.1 Cause: Improper operation can lead to the intake filter breaking and entering the machine, as well as the compressor sucking in large amounts of liquid refrigerant or lubricant, which results in abnormal noises.  10.1.2 Elimination method: The intake filter should be cleaned regularly, and checked for damage.  10.2 Wear of bearings and balance pistons, or friction between the rotor and the casing 10.2.1 Causes: Poor quality of lubricating oil, insufficient oil injection, or the intake of impurities or excessive liquid by the compressor can lead to wear of the moving parts; this is manifested by an increase in operating current, higher temperatures of the casing and exhaust gas, and increased noise.  10.2.2 Elimination methods: The oil coarse and fine filters as well as the intake filter should be cleaned regularly. Before each startup, turn the coupling several times to check for any signs of jamming. 10.3 Too low inhalation pressure. See 9.1 for details.  10.4 Vibration of the slide valve within the engine body 10.4.1 Causes: Under partial load conditions, as the restraint exerted by the rotor or the engine body on the slide valve decreases, the slide valve may vibrate within the engine body, generating noise; this is a normal phenomenon.  10.4.2 Exclusion method: Every effort should be made to prevent the compressor from operating in this state for extended periods.  10.5 Excessive axial deviation between the compressor and the motor; see 9.3 for details.  10.6 Loose key in the coupling 10.6.1 Cause: A loose key in the coupling can result in abnormal noises.  10.6.2 Troubleshooting method: The bolts need to be tightened or the key needs to be replaced.  10.7 Reciprocal movement of the valve disc in non-return exhaust stop valves 10.7.1 Cause: Under partial load conditions, since the exhaust pressure is insufficient to fully overcome the force exerted by the internal spring and the weight of the valve disc, the valve disc may move back and forth within the valve, resulting in noise. This is a normal phenomenon.  10.7.2 Elimination method: As the unit’s energy gradually increases to full load, this noise will gradually disappear.  10.8 Inhaling too much refrigerant liquid – See 9.2 for details. 11 Excessive exhaust temperature or compressor casing temperature. An exhaust temperature of over 90°C in a screw compressor is considered excessive.  Warning: If the exhaust temperature and the temperature of the compressor casing rise rapidly in a short period of time, accompanied by fluctuations in current, the machine should be stopped immediately for inspection. 11.1 Severe overheating of the suction air. 11.1.1 Causes: For compressors with a flooded evaporator design, the superheat of the suction air should be kept between 0.5 and 1°C, while for compressors with a dry evaporator design, it should be maintained between 5 and 15°C. If the superheat of the suction air is too high, as well as the suction air temperature, then the exhaust temperature and the temperature of the compressor casing will also be too high.  11.1.2 Troubleshooting method: Check whether the liquid supply to the evaporator is sufficient, as well as whether the insulation of the return air pipeline is adequate.  11.2 High exhaust and intake pressures: This is mainly manifested as too low intake pressure and too high exhaust pressure; for details, see 1 and 2. 11.3 Severe wear of moving parts, resulting in increased friction: For details, see 7.3. 11.4 Excessively high exhaust pressure: 11.4.1 Reasons: Oil pressure is related to temperature; when the exhaust pressure is too high, the exhaust temperature as well as the temperature of the engine block will increase accordingly.  11.4.2 Exclusion method: At this time, the high-pressure system and the cooling water system need to be checked.  11.5 Insufficient oil or liquid injection by the compressor, or excessive oil temperature 11.5.1 Causes: One of the functions of lubricating oil and refrigerant liquid in the compressor is to cool the gas being compressed; insufficient injection of oil or liquid, or excessive oil temperature, can lead to an increase in the exhaust temperature.  11.5.2 Exclusion methods: To ensure the flow rate of lubricating oil and refrigerant liquid, regularly check whether the oil pressure gauge is functioning properly, whether the oil circuits and injection holes are blocked, and whether the liquid injection pipelines are unobstructed. Also, regularly clean and maintain the coarse oil filter, fine oil filter, liquid injection filter, and oil cooler.  12 Drop in exhaust temperature or oil temperature 12.1 Liquid in the compressor’s suction side 12.1.1 Causes: Excessive liquid supply to the evaporator or a malfunction in the liquid level control in the low-pressure circulation reservoir can lead to liquid in the compressor’s suction side; additionally, an excessively wide opening of the economizer throttle valve can also result in liquid in the suction side at the make-up air port.  12.1.2 Exclusion method: At this time, the supply valve should be closed partially, and the water or fluid inlet to the oil cooler should also be reduced accordingly.  12.2 Continuous low-load operation of the compressor 12.2.2 Troubleshooting methods: The energy slide valve should be adjusted appropriately according to the level of thermal load; it is also necessary to monitor whether automatic load reduction occurs due to leaks in the diaphragm of the energy slide valve.  Note: It is not economical for the machine to operate at 50% load for extended periods of time./ 12.3 Excessive low exhaust pressure 12.3.1 Causes: This situation usually occurs in colder seasons. Screw compressors generally require an exhaust pressure of more than 0.8 MPa; a further decrease in exhaust pressure may affect the liquid supply to the evaporator as well as the speed at which frost is removed by hot gas.  12.3.2 Exclusion methods: The flow rate of cooling water can be reduced as appropriate, or the number of operating condensers and cooling towers can be decreased; for evaporative condensers, the water pumps and fans can also be turned off.  13 The slide valve does not move smoothly or does not move at all. 13.1 The oil circuit is blocked and the oil pressure is too low. 13.1.1 Solution: Clean the coarse and fine oil filters, and check the components related to the oil circuit.  13.2 Failure of the electromagnetic directional control valve and potentiometer 13.2.1 Causes: When the electromagnetic directional control valve is not powered, it is possible to press the fault check button on it in order to check whether the spool is functioning; if it is functioning, then the problem lies with the electromagnetic directional control valve.  1) The electromagnetic coil is burned out. 2) The push rod is stuck or the return spring is broken. 3) Check the outlet and fuses. 4) The inside of the valve is too dirty. 13.2.2 Troubleshooting methods: 1) Replace it. 2) Repair or replace it. 3) Replace it. 4) Clean it. 13.3 Oil piston seal leakage. 13.3.1 Causes: The PTFE seal ring of the oil piston is damaged, aged, or not sealing properly, resulting in oil leakage; this allows the lubricating oil in the load-in and load-out areas of the oil piston cylinder to mix with each other, causing the slide valve to operate inflexibly or not at all.  13.3.2 Elimination method: Replace the sealing ring.  13.4 Jamming of the slide valve, oil piston, slide valve guide rod, screw rod, and displacement transfer rod 13.4.1 Causes: The capacity control and specific volume ratio mechanisms of screw compressors are relatively complex transmission systems; wear or jamming in any of the moving parts that work together, due to poor quality of lubricating oil or the presence of foreign particles, can lead to failures in the overall transmission system.  13.4.2 Exclusion methods: Note: If it is confirmed that the causes are those listed in points 13.3 and 13.4, it is necessary to contact the equipment manufacturer’s professional maintenance personnel for repairs.  14 Energy, specific volume ratio for automatic loading or unloading 14.1 Failure of electromagnetic directional valves and potentiometers 14.1.1 Cause: Oil leaks from the electromagnetic directional valves into the cylinder, pushing the oil piston to shift and causing the compressor to load or unload automatically.  14.1.2 Exclusion methods: Check whether the electromagnetic directional control valve is dirty or blocked and thus not closing properly, whether the film is damaged, and whether there is oil leakage.  14.2 Oil leakage from the piston seal ring 14.2.2 Solution: Replace the seal ring 14.3 Errors in the program control of automatic units 14.3.1 Causes: If there are faults or significant deviations in the temperature sensors or pressure transducers in a microcomputer-controlled unit, or if there are errors in the PLC control program, incorrect commands will be issued, causing the compressor to increase or decrease its load automatically.  14.3.2 Exclusion method: In such cases, a professional should be consulted for diagnosis or the program should be re-entered; the inspection period for the operation of electrical equipment is three months.  15: The cooling capacity of the compressor is insufficient; 15.1: The capacity adjustment indication is incorrect. Depending on the heat load of the evaporator, the slide valve should be adjusted to the appropriate position. However, the energy adjustment indication of the compressor only reflects the corresponding position of the slide valve in a linear manner, and it does not represent the actual cooling capacity of the compressor.  15.1.1 Resolution method: Perform maintenance. 15.2 Low suction pressure; see section 1 for details. 15.3 Gas leakage between high-pressure and low-pressure systems: In units where gas from the high-pressure side leaks to the low-pressure side, this occupies a large volume of space, resulting in less gas being drawn in by the compressor from the evaporator and thus a reduced cooling capacity of the unit.  15.4 Weakened sealing effect of lubricating oil 15.4.1 Reasons: In screw compressors, a certain amount of lubricating oil is injected to create an oil film seal between the rotors as well as between the rotors and the compressor casing, thereby preventing gas from high-pressure areas from leaking to low-pressure areas. If the viscosity of the oil decreases or the amount of oil injected is insufficient, the sealing effect weakens, and the cooling capacity of the compressor declines.  15.4.2 Exclusion method: Note: The oil temperature should be kept within an appropriate range ； When servicing the machine, make sure to check whether the fuel injection holes are clogged.  15.5 Wear of major components inside the compressor 15.5.1 Causes: The entry of foreign objects into the compressor or poor lubrication can lead to wear of the rotor and the compressor casing, as well as an increase in the gaps between the rotors and between the rotors and the casing. This results in increased internal leakage and a decline in the compressor’s cooling capacity. In particular, damage to the axial bearings and balance pistons can cause an increase in the gap at the exhaust end, which has a significant impact on the cooling effect. It may also lead to severe wear between the rotor and the suction end seat.  15.5.2 Troubleshooting methods: Note: It is necessary to clean each filter regularly, and inspect and replace the thrust bearings periodically. The annual inspection period for compressors is one year, while the major repair period is three years.  15.6 Excessively high exhaust pressure; see 11 for details. 15.7 Insufficient evaporator area. 15.7.1 Reason: An insufficient evaporator area prevents the compressor from delivering its full cooling capacity.  15.7.2 Elimination method: The evaporator needs to be replaced.  Leakage in the shaft seal of unit 16. 16.1 Wear of the shaft seal sealing ring, or wear or aging deformation of the O-ring. 16.1.1 Causes: Insufficient oil supply in the shaft seal chamber, as well as mechanical impurities in the oil injected, can lead to wear of the sealing surfaces of the rotating and stationary rings as well as the O-ring. This causes oil leakage from the shaft seal.  16.1.2 Exhaust method: Ensure the oil injection volume for the shaft seal, maintain the correct installation direction of the oil seal, and regularly clean the oil filter.  16.2 Excessively high oil temperature 16.2.1 Causes: If the oil temperature is too high, the viscosity of the oil decreases, which weakens the effectiveness of the oil film; this can lead to leakage at the shaft seals. It also accelerates the aging of the O-rings.  16.2.2 Elimination methods: Controlling oil temperature. 16.3 The oil injected contains a large amount of refrigerant liquid. 16.3.1 Causes: Severe liquid carryover in the compressor’s suction line, or prolonged shutdown periods during winter result in the accumulation of substantial amounts of refrigerant liquid within the oil separator. This liquid fails to vaporize in time; instead, it is drawn by the oil pump and transported to the shaft seal chamber. There, it absorbs frictional heat, evaporates, and expands, causing the stationary and rotating seal rings to separate. This leads to oil leakage, or frequent opening and closing of these rings, resulting in impacts that may cause them to break.  16.3.2 Troubleshooting methods: The liquid supply volume should be adjusted in a timely manner, and the compressor should be unloaded. Additionally, the water inlet valve or liquid inlet valve of the oil cooler should be partially closed; in severe cases, the machine should be shut down.  16.4 Excessive misalignment between the compressor and motor. Please refer to Section 9.3 for details.
16.5 Poor assembly when installing or maintaining the shaft seal.
16.5.1 Causes: Poor assembly of the shaft seal can be caused by excessive planar deviation or damage to the moving and stationary rings during installation or maintenance; seals and O-rings that are too loose, too tight, or deformed; improper assembly of spring seats and push-ring pins; insufficient spring tension, etc.  16.5.2 Troubleshooting method: Replacement or reassembly is required. Note: A slight leakage from the compressor’s shaft seal is normal and helps to prevent wear of the sealing ring. The allowable oil leakage from the shaft seal is 6 drops per minute or 3–5 milliliters per hour; however, if there is a tendency for the leakage to increase, the machine should be shut down for maintenance to prevent further wear of the sealing ring.  17 Oil leakage from the shaft seal of the pre-lubrication pump: Refer to the analysis of oil leakage from the main engine’s shaft seal. To protect the oil pump and its shaft seal, it is necessary to clean the coarse oil filter regularly.  18 The pre-lubrication oil pump is unable to generate sufficient oil pressure. 18.1 The oil level inside the oil container is too low; see 5.1 for details. 18.2 The oil circuit system, as well as the coarse and fine oil filters, are too clogged; see 5.2 for details. Note: It is recommended to clean the coarse oil filter after 72 hours of operation of a newly installed unit; after doing this three times, it should be cleaned every three months of operation.  18.3 Oil pump failure 18.3.1 Causes: Failures of the oil pump motor, wear of the oil pump rotor, and damage to the oil pump coupling can all prevent the oil pump from operating properly.  18.3.2 Exclusion methods: The oil pump motor needs to be inspected, the oil pump rotor must be repaired or replaced, and the oil pump coupling needs to be replaced.  18.4 Misalignment of pressure transmitters or pressure/differential pressure controllers 18.4.4 Troubleshooting methods: These electronic components need to be calibrated or replaced.  19 Noise from the pre-lubrication oil pump 19.1 Damaged oil pump coupling 19.1.1 Solution: Replace it.  19.2 Loose bolts 19.2.1 Solution: Tighten again.  19.3 Oil pump damage 19.3.1 Resolution method: Replace.  20: Decrease in oil level. 20.1: Decrease in exhaust temperature. 20.1.1 Reason: Excessively low suction superheat, liquid in the compressor, resulting in too low exhaust temperature.  20.1.2 Solution: Reduce the throttle valve opening. 20.2 The filter element in the oil filter is not properly secured or is damaged. 20.2.1 Solution: Check it, secure it properly, or replace it. 21: The oil level drops sharply when the machine is stopped. 21.1: The check valves in the suction circuit and those in the economizer’s air supply line do not function properly as check valves. 21.1.1: Solution: Carry out maintenance work.  21.2 Damage to the check valve between the compressor make-up air port and the economizer 21.2.1 Troubleshooting method: Perform maintenance.  22 Rising oil level. 22.1 Oil in the system returns to the compressor. 22.1.1 Reason: In systems where multiple units operate in parallel, the oil consumption of each unit varies; the oil that enters the system is not discharged in time and, after entering the evaporator, it goes along with the suction air into the compressor, causing the oil level to rise.  22.1.2 Exclusion method: If the oil level is high, excess lubricating oil should be drained promptly. For safety reasons, the machine should be shut down while draining the oil.  22.2 Excessive refrigerant entering the oil 22.2.1 Causes: 1) The compressor is shut down for an extended period, and the liquid that condenses in the exhaust pipeline flows into the oil, creating an illusion of an elevated oil level.  2) Additionally, inadequate operation of the check valve in the suction shut-off valve, or damage to the check valve in the economizer make-up air line, can also cause excessive refrigerant to enter the compressor, leading to an increase in the oil level.  22.2.2 Exclusion method: 1) The oil temperature should be increased to cause the refrigerant contained in it to evaporate from the lubricating oil.  2) Carry out maintenance.  22.3 Blockage in the oil outlet pipeline of the oil separator 22.3.1 Resolution method: Carry out maintenance.  23 Reverse rotation of the main unit during shutdown 23.1 Poor sealing of the non-return suction and discharge stop valves 23.1.1 Cause: When the non-return suction and discharge stop valves do not seal properly—especially when the non-return suction stop valve fails to close—the compressor may experience severe reverse rotation upon shutdown.  23.1.2 Troubleshooting method: Perform maintenance to eliminate any jamming issues.  Note: During long periods of shutdown, the check-type suction and exhaust stop valves must be closed, with a maintenance period of two years.  23.2 Obstructed bypass pipeline 23.2.1 Troubleshooting method: Inspect the bypass pipeline and service the solenoid valve installed on it.  24 Suction temperature is too high. Note: Based on the reading of the suction pressure gauge, refer to the thermodynamic properties table to find the corresponding evaporation temperature; compare this with the reading on the suction temperature gauge in order to calculate the suction superheat.  24.1 Insufficient system refrigerant 24.1.1 Troubleshooting methods: 1) First, check for leaks at all pipe joints, flange connections, valve stems, and shaft seals in the system. For ammonia systems, phenolphthalein test paper soaked in water can be used to detect leaks; if the paper turns red, there is a leak ； The ammonia system can be leak-tested using soap or a halogen leak detector.  Warning: Soapy water must not be used to leak-test ammonia systems.  2) Add refrigerant to the specified amount.  24.2 Small throttle valve opening or blocked piping. 24.2.1 Troubleshooting methods: First, adjust the liquid supply throttle valve in the system. If, after increasing the throttle valve opening, there is still no change in the suction pressure and temperature, it is necessary to check whether the relevant valves at the control station are malfunctioning, and whether the piping and filters are blocked. In ammonia systems, pay attention to whether ice blockage has occurred in the throttle valve.  24.3 Poor insulation of the suction piping 24.3.1 Remedy: The low-temperature return gas piping in the refrigeration system must be properly insulated. The presence of frost or dripping at the insulated joints or on the packaging surface indicates poor insulation. Overheating of the suction air caused by poor insulation is known as harmful overheating; it leads to a loss of cooling capacity in the system, and it should be monitored continuously and addressed promptly.  24.4 Moisture content exceeds the specified limit. 24.4.1 Remedy: Check the moisture content.  25 Abnormal frost formation on the compressor head 25.1 Excessive opening of the thermal expansion valve 25.1.1 Solution: Adjust the valve to a smaller opening.  25.2 Insufficient heat load 25.2.1 Resolution methods: Reduce the liquid supply or reduce the compressor load.  25.3 The temperature sensing bulb of the thermal expansion valve is not securely tied or is tied in the wrong position. 25.3.1 Troubleshooting method: Retie it as required.  26 Oil temperature fluctuations: The operating conditions of the system vary greatly; it is necessary to stabilize these conditions.  27 Excessively high suction pressure 27.1 Throttle valve opened too wide 27.1.1 Solution: Adjust the valve to a smaller opening.  27.2 The temperature sensing bulb of the thermal expansion valve is not tied tightly or the tying position is incorrect; see 25.3 for details.      Installing the coupling: First, fit a retaining ring on the motor shaft, then install half of the coupling. Next, place retaining blocks at the pump shaft end and within the coupling slots, and tighten the bolts using a ring wrench (lift the pump shaft by 3–5 millimeters to apply preload to the mechanical seal) ； Install the other half of the coupling as well and tighten the hex screws – they must be tightened properly. Correct inspection requirements for coupling installation: The gap above and below the split coupling should be even ； Turn the coupling by hand several times to check that it rotates smoothly.