Common faults and maintenance methods of air curtain cabinet compressors
1. Foreword
The air source heat pump unit is With its own cold and heat source, easy installation and other characteristics, it has been widely used in recent years; however, due to the influence of air conditioning load and external environment, the working range fluctuates greatly, and the unit runs for a long time under non-standard conditions. Under severe working conditions, some compressor failures occurred in the unit. This paper makes a detailed analysis of some compressor failure problems in the actual operation of the air source heat pump unit, and proposes corresponding improvement measures.
2. Fault phenomenon There are many types of compressors used in air source heat pump units, with fully enclosed piston compressors being the most common, and the failure problems of fully enclosed piston compressors mostly occur During heating operation in winter. By observing the failure situation of some faulty compressors, the faults of the compressors can be roughly divided into three categories:
(1) The compressor suction and discharge valve plates are ruptured and the oil level of the compressor is normal. , The bearing, crankshaft and connecting rod of the compressor are in good condition, and the suction and exhaust valve plates are broken.
(2) Compressor stall phenomenon The compressor refrigeration oil is black, the upper and lower bearing sleeves fall off or are worn, the connecting rod is broken, the friction surface between the crankshaft and the bearing and the friction surface between the crankshaft and the connecting rod have scratches , There are wear marks on the rotor of the motor, and the suction and exhaust valves are in good condition.
(3) Burnout of compressor motor The insulation of the compressor to the ground is 0, and the bearing, crankshaft and connecting rod of the compressor are intact.
3. Analysis of common faults of air curtain cabinet compressors
(1) The rupture of the suction and exhaust valves of the compressor can be seen from the fault phenomenon, causing compression The main reason for the rupture of the suction and exhaust valve of the machine is the rupture of the water side system of the unit. The rupture of the water-side system is mainly due to the phenomenon that the water system is interrupted when the unit is in refrigeration operation. Because some users have short-circuited the flow switch without permission, the unit cannot perform protection action, and the water-side heat exchanger (especially the flooded heat exchanger) The internal water freezes and causes the heat exchange copper tube to freeze and crack, so that the water and fluorine are mixed with each other, and the water enters the compressor to form liquid hammer and cause damage.
(2) Motor burnout As mentioned above, liquid backflow is the main factor that causes the shaft to be held. The bearing eccentricity caused by the shaft holding will cause the motor stator to wear and cause the motor to short-circuit and burn out. However, for pure motor burnout, the cylindrical structure of the fully enclosed piston compressor determines that it is not sensitive to liquid shock. Even if some liquid refrigerant enters the compressor, it will generally not directly cause the valve plate to break, nor It will directly cause the motor to burn out.
At the same time, because the lubrication of hermetic compressors is mostly centrifugal splash type, there is no control of pressure difference, so the compressor can also run in the case of lack of oil lubrication. At this time, the compressor current continues to rise until the air switch (overcurrent protector) trips. This process is due to the overload operation of the compressor, the current is large, and the temperature rise of the motor coil is also very fast, until the embedded PTC operates. Because the PTC temperature rise rate of the compressor is very sensitive under full load or overload conditions, and the air switch operates before the PTC, there is no basis for the motor to burn out directly due to lack of oil.
We believe that there are two reasons why the motor of the compressor burns out:
①The interior of the refrigeration system is not clean, contains impurities, and the impurities are corroded and worn Motor coil, resulting in short circuit and burnt out.
②The motor temperature rise is too high. Because the motor of the hermetic compressor is cooled by the return air, when the heat pump is heated in winter, the working conditions are relatively poor, especially when the ambient temperature is very low, the heat exchange is small, the refrigerant circulation is also small, and the return air pressure is small. Low, coupled with untimely and incomplete defrosting on the electronic control, will lead to insufficient cooling of the motor and heating of the coil. Such continuous heating will result in high temperature, and PTC is not sensitive to the small current response at low load, so after the compressor is started several times, the insulation will be damaged due to overheating and the motor will be short-circuited and burned before reaching a higher temperature.
(3) Compressor locked rotor From the anatomy of such faulty compressors, there is no shortage of oil inside the compressor, and the locked shaft is caused by instantaneous poor lubrication, which is the main cause of poor lubrication. The reason is that the oil quality of the lubricating oil has changed, the oil is diluted or the oil level is raised by the refrigerant liquid.
The reasons for the liquid backflow of the unit are:
①The refrigerant in the refrigeration cycle usually accumulates in the part with the lowest temperature and is condensed. When the unit is shut down for a long time, because the heat capacity of the compressor is larger than that of the condenser, evaporator, and accumulator, the compressor becomes the part with the lowest temperature in the refrigeration cycle, allowing the refrigerant to enter. Since the lubricating oil can dissolve the refrigerant well, the refrigerant accumulated in the compressor is dissolved in the lubricating oil. This phenomenon is called “dissolving” phenomenon. The amount of refrigerant “dissolved” varies depending on the amount of refrigerant charged, the structure of the refrigeration cycle and the length of downtime. When it is saturated, it is roughly 30-100% of the amount of lubricating oil charged. Diluted oil can cause poor lubrication and cause shaft seizure. Furthermore, if the unit is stopped for a long time, the lubricating oil will separate into the liquid phase depending on the temperature of the closed casing of the compressor, the type of refrigerant and lubricating oil, and is divided into refrigerant liquid (more refrigerant, refrigerant and lubricating oil) in the lower part. This is the case when the mixture of lubricating oil is small) and the upper part is lubricating oil (there is a lot of lubricating oil, and the mixture of lubricating oil and refrigerant is small). If the compressor is started in such a state, the oil supplied to the bearings and other moving parts is almost only the “lubricant” of the refrigerant liquid. Therefore, in a short time after starting, the bearing parts, connecting rods and other parts Seizing and wear will occur. When the compressor is not preheated before starting, or the preheating time is not enough, and the power of the electric crankcase heater is not enough, the above situation cannot be avoided, resulting in damage to the compressor.
②When the unit is in heating operation, especially in a high humidity environment, the fins are easy to receive frost. If the defrosting method is not too perfect, it cannot be defrosted in time or the defrosting is incomplete. , will cause the low pressure to be low, and the compressor will return to a large amount of liquid, causing the compressor to fail.
4. Improvement measures For the reasons analyzed above, we make corresponding improvement measures
(1) Improve the system design, especially in the low temperature system. Under hot working conditions, the expansion valve and the gas-liquid separator should be matched reasonably, or measures such as adding high and low pressure bypasses should be taken to prevent the liquid return problem of the unit.
(2) There should be an anti-freezing control function in the control (that is, in the shutdown state, when the ambient temperature is lower than a certain value, the water pump or electric heating should be put into operation to prevent freezing of the waterproof system), and at the same time, There should be a drainage device on the water system. When the unit is not used for a long time, the water in the water exchanger should be drained to prevent freezing.
(3) In the electronic control program, the conditions for ensuring the heating time of the compressor crankcase heater before starting the machine are added to ensure that the compressor can be fully preheated to prevent damage.
(4) Improve technology, strengthen management and enhance quality awareness to ensure that the interior of the refrigeration system is clean and free of moisture. The quality of manufacturing and processing is an important factor affecting the quality of the unit. Many problems must be prevented before they occur. cause major failures.
(5) In order to ensure the normal operation of the unit, the flow switch and various protection switches cannot be short-circuited without permission; when the unit is running, it is necessary to observe frequently, and when the temperature difference between the inlet and outlet of the unit is found to be too large, Into the water system in time to check whether the water pump is normal, the water flow and clean the water filter.
(6) Strengthen the user’s use, operation and maintenance training.
(7) Improve the defrosting method, ensure timely defrosting and complete defrosting, improve the reliability of electronic control, and prevent malfunction or non-operation.
