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Analysis of 10 common faults in refrigeration system maintenance and debugging

1. The exhaust temperature of the refrigeration system is too low

Exhaust pressure is too low, although the phenomenon is manifested in the high pressure side, but the cause is mostly at the low pressure side. The reasons are:

1. The expansion valve hole is blocked, the liquid supply is reduced or even stopped, and the suction and exhaust pressures are reduced at this time.

2. The expansion valve is blocked by ice or dirty, and the filter is blocked, which will inevitably reduce the suction and exhaust pressure; the refrigerant charge is insufficient;

2. Refrigeration system finds liquid backflow

1. For small refrigeration systems using capillary tubes, excessive liquid addition will cause liquid backflow. When the evaporator is heavily frosted or the fan fails, the heat transfer becomes poor, and the unevaporated liquid will cause liquid backflow. Frequent temperature fluctuations will also cause the expansion valve to fail to respond and cause liquid backflow.

2. For refrigeration systems using expansion valves, liquid return is closely related to the selection and improper use of expansion valves. Excessive selection of the expansion valve, too small superheat setting, incorrect installation of the temperature sensing package or damage to the thermal insulation wrapping, or failure of the expansion valve may cause liquid backflow.

For refrigeration systems where liquid backflow is difficult to avoid, installing gas-liquid separator control can effectively prevent or reduce the harm of liquid backflow.

3. The suction temperature of the refrigeration system is high

1. The suction temperature is too high due to other reasons, such as poor insulation of the return gas pipeline or too long pipeline, which can cause the suction temperature to be too high. Under normal circumstances, the compressor cylinder head should be half cool and half hot.

2. The refrigerant charge in the system is insufficient, or the opening of the expansion valve is too small, resulting in insufficient refrigerant circulation in the system, less refrigerant entering the evaporator, high superheat, and high suction temperature.

3. The filter screen of the expansion valve port is blocked, the liquid supply in the evaporator is insufficient, the amount of refrigerant liquid is reduced, and a part of the evaporator is occupied by superheated steam, so the suction temperature rises.

4. Liquid

1, should avoid the suction temperature is too high or too low. Excessive suction temperature, that is, excessive superheat, will cause the compressor discharge temperature to rise. If the suction temperature is too low, it means that the refrigerant is not fully evaporated in the evaporator, which not only reduces the heat exchange efficiency of the evaporator, and the suction of wet steam will also form a liquid shock in the compressor. Under normal circumstances, the suction temperature should be 5-10°C higher than the evaporating temperature.

2. In order to ensure the safe operation of the compressor and prevent the occurrence of liquid hammer, the suction temperature is required to be higher than the evaporation temperature, that is, it should have a certain degree of superheat.

5. Start the refrigeration system with liquid

1. The phenomenon that the lubricating oil in the compressor foams violently is called starting with liquid. Foaming during start-up with liquid can be clearly observed on the oil sight glass. The fundamental reason is that a large amount of refrigerant dissolved in the lubricating oil and sinking under the lubricating oil suddenly boils when the pressure is suddenly reduced, and causes the foaming phenomenon of the lubricating oil, which is easy to cause liquid hammer.

2. The installation of crankcase heater (electric heater) in the compressor can effectively prevent the migration of refrigerant. Shut down for a short time to keep the crankcase heater energized. After long-term shutdown, heat the lubricating oil for several or ten hours before starting the machine. Installing a gas-liquid separator on the return gas pipeline can increase the resistance of refrigerant migration and reduce the migration amount.

6. Oil return in refrigeration system

1. Lack of oil will cause serious lack of lubrication. The root cause of oil shortage is not how much and how fast the compressor runs, but the poor oil return of the system. Installing an oil separator can quickly return oil and prolong the operation time of the compressor without oil return.

2. When the compressor is higher than the evaporator, the oil return bend on the vertical return pipe is necessary. The oil return trap should be as compact as possible to reduce oil storage. The spacing between the oil return bends should be appropriate. When the number of oil return bends is large, some lubricating oil should be added.

3. Frequent startup of the compressor is not conducive to oil return. Because the continuous operation time is very short, the compressor stops, and there is no time to form a stable high-speed airflow in the return pipe, so the lubricating oil can only stay in the pipeline. If the return oil is less than the run oil, the compressor will be short of oil. The shorter the running time, the longer the pipeline, the more complex the system, the more prominent the oil return problem.

7. Evaporation temperature of refrigeration system

The cooling efficiency has a greater impact on the cooling efficiency. For every 1 degree decrease, the power needs to be increased by 4% to obtain the same cooling capacity. Therefore, when conditions permit, it is beneficial to increase the evaporating temperature appropriately to improve the refrigeration efficiency of the air conditioner.

The evaporating temperature of the household air conditioner is generally 5-10 degrees lower than the air outlet temperature of the air conditioner. During normal operation, the evaporating temperature is 5-12 degrees, and the air outlet temperature is 10-20 degrees.

Blindly lowering the evaporation temperature can cool the temperature difference, but the cooling capacity of the compressor is reduced, so the cooling speed is not necessarily fast. What's more, the lower the evaporating temperature, the lower the cooling coefficient, but the load increases, the operation time is prolonged, and the power consumption will increase.

Eight, the exhaust temperature of the refrigeration system is too high

The main reasons for the high exhaust temperature are as follows: high return air temperature, large heating capacity of the motor, high compression ratio, high condensing pressure, adiabatic index of refrigerant, and improper selection of refrigerant.

Nine, refrigeration system fluoride

1. When the amount of fluorine is low or its regulating pressure is low (or partially blocked), the bonnet (bellows) of the expansion valve and even the liquid inlet will be frosted; when the amount of fluorine is too small or basically free of fluorine, the appearance of the expansion valve No response, only the slightest sound of airflow can be heard.

2. Look at which end the icing starts, whether it is from the dispenser head or from the compressor back to the trachea. If the dispenser head is deficient in fluorine, the compressor means there is too much fluorine.

10. The suction temperature of the refrigeration system is low

1. Expansion valve opening is too large. Because the temperature sensing element is too loosely bound, the contact area with the return air pipe is small, or the temperature sensing element is not wrapped with thermal insulation material and its wrapping position is wrong, etc., the temperature measured by the temperature sensing element is inaccurate, and it is close to the ambient temperature, which makes the expansion valve act. The opening degree is increased, resulting in excessive liquid supply.

2. The refrigerant charge is too much, which occupies part of the volume of the condenser and increases the condensing pressure, and the liquid entering the evaporator increases accordingly. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked by the compressor contains liquid droplets. In this way, the temperature of the return gas pipeline decreases, but the evaporation temperature does not change because the pressure does not drop, and the degree of superheat decreases. There is no significant improvement even if the expansion valve is closed.