Copeland Scroll Compressor FAQ

   Common fault phenomenon and cause analysis of Copeland scroll compressor

     I. Copeland refrigeration compressor units are widely used in refrigeration equipment such as cold storage. During the use process, there are mainly the following four kinds of failure phenomena:

  1. The floating sealing ring is damaged, and the high and low pressures are leaking.

   According to the structural characteristics of the scroll compressor, in order to provide an appropriate gas pressure on the upper part of the scroll stator, an intermediate pressure channel is opened at an appropriate intermediate compression position on the scroll stator to provide an intermediate pressure. There is a floating sealing device on the upper part of the intermediate pressure chamber, so the top of the scroll is affected by the exhaust pressure and the intermediate pressure. In addition to balancing the compressed gas pressure inside the scroll, it also provides a sealing force between the top and bottom grooves, which is achieved by a floating seal. The sealing ring is made of a non-metallic material similar to rubber or plastic. The fault phenomenon generally shows that the compressor motor is in good condition and can be powered on, but the exhaust pressure of the unit does not increase, the suction pressure does not decrease, there is almost no pressure difference between the suction and exhaust, the exhaust pipe is not hot, and the suction The tube is not cold either. The compressor current is very different from the rated value, in fact the compressor is idling.

  2. The scroll is damaged.

  In addition to the above-mentioned damage to the floating seal ring, the scroll damage can also hear the obvious metal impact sound inside the compressor. The sound of the shell hitting.

  3. The motor burned out.

  When the power is turned on, the fuse is blown or the short circuit is tripped, and the compressor cannot be started.

  4. The motor holds the shaft and the bearing is damaged

  When the compressor is powered on, the motor in the casing is heard humming, but it does not run, and the current rises rapidly. After a few seconds, the compressor's internal overload protection or external thermal relay protection acts, Cut off the power. Sometimes the protector is too late to act, and the locked-rotor current is quickly reached, which may directly cause the motor to burn out.

     II. Failure cause analysis and preventive measures

  1. After dissection of the faulty compressor, it was found that the sealing ring was partially melted or broken

  The reason is: due to refrigerant leakage and other reasons, the suction pressure is reduced (but even if the low pressure protection device is installed, it may not reach the protection set value, and the low pressure protection has not been cut off), the suction superheat degree If the temperature of the exhaust gas is increased, the exhaust temperature will rise rapidly. At this time, if the exhaust temperature protector is not installed or installed improperly, the system will have a serious overheating phenomenon. An effective way to avoid thermal damage to the sealing ring is to install the exhaust temperature protector correctly. The temperature setting of the exhaust temperature protector is generally 125-130 °C; the temperature sensor of the exhaust temperature protector is generally installed on the exhaust pipe of the compressor, and the distance from the exhaust port is no more than 150 mm. The pipe should be fixed firmly, and it needs to be strictly insulated; the wiring of the exhaust temperature protector can be connected in series with other protection measures of the compressor (such as high pressure protection or low pressure protection) to form the protection of the compressor together.

  2. Scroll damage is generally caused by liquid hammer

  There are three main situations: one is that a large amount of refrigerant liquid enters the compressor at the moment of startup; the other is that the water flow of the evaporator is not enough (evaporation load is reduced), and the compressor has a phenomenon of liquid backflow; the third is that the unit heat pump If the defrosting operation is not good, a large amount of liquid refrigerant enters the compressor without evaporating, or the liquid in the instantaneous evaporator of the four-way valve reversing (condenser when the heat pump is running) enters the compressor. Solve the problem of liquid hammer or liquid back, mainly from the following aspects.

  a. The piping design should prevent liquid refrigerant from entering the compressor during startup, which may require an excess liquid return test on the system, especially for refrigeration systems with a relatively large charge. Adding a gas-liquid separator at the compressor suction port is an effective solution to this problem, especially in heat pump units that use reverse cycle hot gas defrosting.

  b. Before starting the machine, preheating the compressor oil pool for a long time can effectively prevent a large amount of refrigerant from accumulating in the compressor lubricating oil. It also has a certain effect on preventing liquid shock.

  c. The flow protection of the water system is indispensable, so that when the water flow is insufficient, it can protect the compressor, so as to prevent the unit from returning to the liquid or freezing the evaporator in severe cases. When the flow switch is damaged, it should be repaired or replaced in time, and the flow switch must not be short-circuited.

  3. The burning of motor windings is related to the protection of electrical design, or caused by improper operation and use of the unit.

  Because the evaporator freezes and cracks, after the fluorine system and the water system collude, the compressor enters the water and causes the compressor to burn out. The reasons are:

  a. Due to various reasons (dirty water filter, unreasonable water pump matching, etc.), the flow rate of the water system is small, and the water flow protection fails or is short-circuited, and the refrigerant copper tube of the evaporator freezes and cracks;

  In winter, the water system of the unit stores water without taking anti-freezing measures, and the evaporator freezes and cracks.

  1) Abnormal load. Frequent action of the built-in thermal protector of the compressor may cause the contacts of the compressor to stick and make the protector useless, thereby burning the motor. Lubrication failure and increased frictional resistance are the main reasons for abnormal load. To solve the problem of lubrication failure, we mainly start from the following aspects: prevent liquid backflow, prevent lubricating oil from overheating (high exhaust temperature), and solve the problem of system oil return or lack of oil.

  2) If the electrical design has no overload protection or overcurrent protection, there may be the following dangers: If the compressor current is large, the motor windings continue to work at a higher temperature, and this temperature is not enough for the built-in thermal protection In this case, the insulation layer of the coil may be damaged and the motor may be short-circuited and burned. Adding external overload protection is an effective means to prevent motor burnout, such as thermal relay protection. The setting value of the thermal relay should be able to open when not exceeding 140% of the rated current of the compressor. In addition, it is also very important for the power cord of the unit to pass through the air switch.

  3) There are impurities in the system, which corrode and wear the compressor motor coil, causing the motor to burn out.

  4) The frequent start and stop of the motor will make the contactor contacts of poor quality prone to sticking. In this way, relying on the contactor to disconnect all the protection controls (high and low pressure protection, exhaust temperature protection, Water flow protection, etc.) will all fail, and the compressor will be in an unprotected state, causing the motor to burn out. Therefore, the contactor should be selected correctly.

  5) Insufficient cooling is also one of the reasons for the burnout of the compressor motor. Hermetic scroll compressors are generally cooled by refrigerant, and a large amount of refrigerant leakage will cause insufficient cooling of the compressor. Of course, a large amount of refrigerant leakage will generally cause low pressure protection or thermal protection, but if the low pressure protection and thermal protection fail, it will cause the compressor to burn out.

  4. The motor holds the shaft, and the root cause of bearing damage is the lubrication problem. There are the following situations:

  1). There is not enough lubricating oil, or there is a problem with the oil return of the system. In this case, the bearing cannot be fully lubricated, and the bearing wear will increase, which will cause the motor to hold the shaft. Therefore, the mass ratio of refrigeration oil to refrigerant is generally required to be greater than 0.35, otherwise refrigeration oil must be supplemented. In addition, the on-site replacement of the compressor will also cause the loss or deterioration of the refrigeration oil. At this time, part of the refrigeration oil needs to be replenished.

  2). Impurities in the system enter the bearing, and the bearing is worn or stuck, causing the motor to hold the shaft. According to the analysis of relevant researchers, the main components of impurities are copper, iron, carbides, etc., which are mainly generated during the production process, such as solder bumps or welding slag entering the copper tube during brazing; copper scraps when the copper tube is cut Into the system; poor lubrication during the operation of the compressor will increase the high temperature caused by friction, and the high temperature will cause the carbonization of the lubricating oil or other organic matter; the system is not completely evacuated, there is moisture, or the moisture control in the refrigerant is not pure enough, the moisture It will cause "copper plating" in the system, which will cause powdery copper and iron particles in the system; the workplace is not clean, and dust and impurities enter the system. In response to these problems, the production process should be improved, the discipline of the process should be strictly enforced, and the technical level of the workers should be improved.

  3). There is no preheating or the preheating time is not enough before starting, which causes a large amount of refrigerant in the system to migrate to the compressor, and the liquid refrigerant accumulates in the compressor, and the density of the liquid refrigerant is higher than that of the refrigeration oil. Therefore, the refrigerant accumulated at the bottom of the compressor is divided into two layers, the upper part is the refrigeration oil (oil-rich phase), and the lower part is the refrigerant (refrigerant-rich phase). The refrigerant in the lower part prevents the refrigerant oil from entering the bearing lubrication area (equivalent to raising the refrigerant oil level), and almost all refrigerant enters the bearing lubricating surface at startup, resulting in poor lubrication and foam. If the refrigerated oil and liquid refrigerant enter into the compression chamber, it will also cause liquid compression.

  An effective measure to prevent refrigerant migration and dissolution in lubricating oil is to use a heater. By heating the oil, the temperature of the oil is higher than that of other parts of the system, and the refrigerant in the lubricating oil evaporates, but The power of the oil heater should not be too high, otherwise the oil will be overheated, the viscosity will be reduced, and even carbonized, which will also cause improper bearing lubrication. Therefore, the oil heater should be selected correctly.

  Another problem is that even if the unit is designed with a heater, in actual application, some users tend to ignore this point, resulting in frequent occurrences of no preheating or insufficient preheating time before starting up. Therefore, if If possible, it is recommended to set it on the electrical control system to ensure sufficient warm-up time. When the preheating time is generally 12--24 h, the oil temperature should be 10-12 °C higher than the ambient temperature.