The refrigeration system is a general term for the equipment and pipes through which the refrigerant flows, including compressors, condensers, throttling devices, evaporators, pipes and auxiliary equipment. It is the main component system of air conditioning equipment, cooling and refrigeration equipment.
The blockage fault of the refrigeration system has various forms such as ice blockage, dirty blockage and oil blockage. The unified fault characteristics of blockage are: the condenser is not hot, the evaporator is not cold, the compressor running current is smaller than normal, and the pressure gauge is connected to the On the bypass charging valve, the indication is negative pressure, the running sound of the outdoor unit is light, and the sound of liquid passing through the evaporator cannot be heard.
Causes and faults of ice blockage
The occurrence of ice blockage failure is mainly due to the excessive moisture in the refrigeration system. With the continuous circulation of the refrigerant, the moisture in the refrigeration system gradually concentrates at the outlet of the capillary tube. Since the temperature at the outlet of the capillary tube is the lowest, the water freezes into ice and gradually increases. If it increases, the capillary tube will be completely blocked to a certain extent, the refrigerant cannot be circulated, and the refrigerator will not cool.
The main source of moisture in the refrigeration system is: the motor insulating paper in the compressor contains moisture, which is the main source of moisture in the system. In addition, the components of the refrigeration system and the connected pipes are left with moisture due to insufficient drying; the refrigerating machine oil and refrigerant contain more than the allowable amount of moisture; during the assembly or maintenance process, the pipes are in a state of development for a long time, resulting in the moisture in the air being removed. Absorbed by motor insulation paper and refrigeration oil. Due to the above reasons, the water content of the refrigeration system exceeds the allowable amount of the refrigeration system, resulting in ice blockage. On the one hand, ice blockage makes the refrigerant unable to circulate, and the refrigerator cannot cool normally; on the other hand, the water will chemically react with the refrigerant to generate hydrochloric acid and hydrogen fluoride, which will cause corrosion to metal pipes and components, and even lead to motor windings. The insulation is damaged, and it will also cause the deterioration of the refrigeration oil, which will affect the lubrication of the compressor. Therefore, the moisture in the system must be kept to a minimum.
The performance of ice blockage in the refrigeration system is that the initial stage is working normally, the evaporator is frosted, the condenser is dissipating heat, the unit runs smoothly, and the sound of the refrigerant movement in the evaporator is clear and stable. With the formation of ice blockage, the audible airflow gradually becomes weaker and intermittent. When the blockage is serious, the airflow sound disappears, the refrigerant circulation is interrupted, and the condenser gradually cools down. Due to the blockage, the exhaust pressure rises, the running sound of the machine increases, there is no refrigerant flowing into the evaporator, the frosting area gradually becomes smaller, the temperature gradually increases, and the capillary temperature also rises together, so the ice cubes begin to melt. The refrigerant starts to circulate again. After a period of time, the ice blocking occurs again, forming a periodic open-blocking phenomenon.
Causes and faults of dirty blockage
Dirty blockage failures are caused by excess impurities in the refrigeration system. The main sources of impurities in the system are: dust and metal shavings during the manufacturing process of the refrigerator, the oxide layer on the inner wall surface falls off when the pipeline is welded, the inner and outer surfaces of each component are not cleaned during the processing, and the pipeline is not tightly sealed Dust enters In the tube, the refrigerating machine oil and refrigerant contain impurities, and the desiccant powder of poor quality in the drying filter. When these impurities and powders flow through the drier filter, most of them are removed by the drier filter. When there are many impurities in the drier filter, some fine dirt and impurities are brought into the capillary tube by the refrigerant with a higher flow rate, and in the curved section of the capillary tube The parts with larger resistance stay and accumulate, and the resistance becomes larger and larger, which makes it easier for impurities to stay until the capillary is blocked and the refrigeration system cannot circulate. In addition, the distance between the capillary tube and the filter screen in the filter drier is too close to cause dirty blockage failure; in addition, it is also easy to weld the capillary tube mouth when welding the capillary tube and the filter drier.
After the refrigeration system is dirty and blocked, because the refrigerant cannot be circulated, the compressor runs continuously, the evaporator is not cold, the condenser is not hot, the compressor shell is not hot, and there is no airflow in the evaporator. If partially clogged, the evaporator will feel cool or icy, but not frosted. The outer surfaces of the filter drier and capillary were cold to the touch, frosted, or even hoarfrost. This is because when the refrigerant flows through the micro-blocked filter drier or capillary, throttling and depressurization will occur, so that the refrigerant flowing through the blockage will expand, vaporize, and absorb heat, resulting in condensation or condensation on the outer surface of the blockage. Frost.
The difference between ice blockage and dirty blockage: after the ice blockage occurs for a period of time, the refrigeration can be resumed, forming a period of time of opening, blockage for a while, and a periodical repetition of the blockage and the blockage. And after the dirty blockage occurs, it cannot be cooled.
In addition to the dirty blockage of the capillary, if there are too many impurities in the system, the drying filter will gradually be blocked. Because the filter itself has a limited capacity to filter out the dirt and impurities, blockage will occur due to the continuous accumulation of impurities.
Oil plug failure and other line blockage failures
The main reason for the oil blockage in the refrigeration system is the serious wear of the compressor cylinder or the excessive clearance between the piston and the cylinder.
The gasoline discharged from the compressor is discharged into the condenser, and then enters the drying filter together with the refrigerant. Due to the high viscosity of the oil, it is blocked by the desiccant in the filter. The refrigerant does not circulate properly, and the refrigerator does not cool.
The reasons for the blockage of other pipelines are: when the pipeline is welded, it is blocked by solder; or the replaced pipe itself is blocked and not found when the pipe is replaced. The above blockage is caused by human factors, so it is required to weld and replace the pipe. , it should be operated and checked as required, so that it will not cause artificial blockage failure.
How to eliminate blockage in refrigeration system
一、Troubleshooting of ice blockage
The ice block failure of the refrigeration system is due to the excess moisture in the system, so the entire refrigeration system must be dried. There are two processing methods:
1. Use a drying oven to heat and dry the components, remove the compressor, condenser, evaporator, capillary, and air return pipe in the refrigerant system from the refrigerator, and put them into the drying oven for heating and drying. The temperature in the oven is About 120 ℃, drying time is 4 hours, after natural cooling, blow drying with nitrogen one by one. Replace the filter drier with a new one, and then you can assemble and weld, press for leak detection, vacuumize, fill with refrigerant, test run and seal. Using this method to eliminate ice blockage is the best, but it is only applicable to the warranty department of the refrigerator manufacturer. Generally, the repair department can use methods such as heating and evacuation to eliminate the ice blockage fault.
2. Use heating and vacuuming and secondary vacuuming to remove moisture from each component of the refrigeration system.
二、Troubleshooting of Dirty Blockage
There are two ways to eliminate the capillary blockage failure: one is to use high-pressure nitrogen gas combined with other methods to blow out the dirt of the blocked capillary tube. After the capillary tube is blown through, after cleaning and drying the various components in the refrigeration system, reassemble and weld the fault. exclude. If the capillary is seriously blocked and the above method cannot eliminate the fault, the method of replacing the capillary is used to eliminate the fault, as follows:
1. Blow out the dirt in the capillary tube with high-pressure nitrogen: cut the process tube to discharge the liquid, weld the capillary tube from the drying filter, connect the three-way repair valve to the compressor process tube, and fill it with high pressure of 0.6-0.8MPa Nitrogen, and straighten the capillary tube and heat it with a gas welding carbonization flame to carbonize the dirt in the tube, and blow out the dirt in the capillary tube under the action of high-pressure nitrogen. After the capillary was unblocked, 100 ml of carbon tetrachloride was added for aeration cleaning. The cleaning of the condenser can be cleaned with carbon tetrachloride on the pipe cleaning device. Then replace the filter drier, fill with nitrogen for leak detection, vacuumize, and finally fill with refrigerant.
2. Replacing the capillary: If the dirt in the capillary cannot be flushed out by the above method, the capillary can be replaced together with the low-pressure tube. First, remove the low-pressure tube and capillary tube from the copper-aluminum joint of the evaporator by gas welding. When disassembling and welding, the copper-aluminum joint should be wrapped with wet cotton yarn to prevent the aluminum tube from being burned out by high temperature.
When replacing the capillary, flow measurement should be carried out. The outlet of the capillary should not be welded with the inlet of the evaporator first, and a management valve and a pressure gauge should be installed at the inlet and outlet of the compressor. After the compressor is running, the air will be sucked from the low-pressure repair valve. When the outside atmospheric pressure is equal, the indicated pressure of the high pressure gauge should be stable at 1-1.2MPa. If the pressure exceeds, indicating that the flow is too small, a section of capillary can be cut off until the pressure is suitable. If the pressure is too low, it means that the flow rate is too large. The capillary can be coiled several times to increase the resistance of the capillary, or a capillary can be replaced. After the pressure is suitable, the capillary is welded to the inlet pipe of the evaporator.
When welding a new capillary, the length of the copper-aluminum joint should be about 4-5cm to avoid welding blockage. When the capillary is welded with the filter drier, the insertion length is preferably 2.5cm. If the capillary is inserted too much into the filter drier and is too close to the filter screen, tiny molecular sieve particles will enter the capillary and block it. If the capillary is inserted too little, impurities and molecular sieve particles during welding will enter the capillary and directly block the capillary channel. Therefore, the capillary is inserted into the filter, neither too much nor too little. Too much or too little creates a risk of clogging. Figures 6-11 show the connection position between the capillary and the filter drier.
三、Troubleshooting of oil plugs
The occurrence of oil plugging failure indicates that there is too much refrigerating machine oil remaining in the refrigeration system, which affects the refrigeration effect, or even fails to refrigerate. Therefore, the refrigerating machine oil in the system must be cleaned up.
When the oil of the filter is blocked, a new filter should be replaced, and at the same time, part of the refrigeration oil accumulated in the condenser is blown out with high-pressure nitrogen, and the condenser can be heated by an electric blower when nitrogen is introduced.
Shanghai KUB Refrigeration Equipment Co., Ltd.
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