Analysis of 10 major failure phenomena commonly seen in refrigeration equipment maintenance 2019-07-05

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


The low exhaust pressure is mainly caused by the small or even stop flow of the refrigerant in the refrigeration system. The exhaust pressure is too low, although the phenomenon is manifested at the high pressure end, but the cause is mostly caused by the low pressure end.


Common reasons for low exhaust pressure:

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

2) The expansion valve ice block or dirty blockage and filter blockage, etc., will inevitably reduce the suction and exhaust pressure.


2. Refrigeration system back to liquid:


1) For a small refrigeration system using a capillary: the liquid addition is too large to cause liquid return. When the evaporator is severely frosted or the fan fails, the heat transfer deteriorates, and the unvaporized liquid causes the liquid to return. Frequent fluctuations in temperature can also cause the expansion valve to fail to react and cause back flow.

2) For refrigeration systems using expansion valves: liquid return is closely related to the selection and use of expansion valves. If the expansion valve is too large, the super heat setting is too small, the installation method of the temperature sensor package is incorrect, or the insulation package is damaged, and the expansion valve fails, the liquid return may occur.


For refrigeration systems that are difficult to avoid with liquid return, the installation of gas-liquid separator control can effectively prevent or reduce the hazard of liquid return.


3. The intake temperature of the refrigeration system is high:


1) If the return air pipe is not well insulated or the pipe is too long, it can cause the intake temperature to be too high. Under normal circumstances, the cylinder head of the compressor should be half cold and half hot.

2) The refrigerant charge in the system is insufficient. Or the expansion valve opening degree is too small, resulting in insufficient circulation of the refrigerant of the system, the refrigerant amount of the evaporator is small, the degree of super heat is large, and the intake temperature is high.

3) The expansion valve port is clogged. The amount of 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 intake air temperature is increased.


4. Liquid stroke:


1) Avoid inhalation temperatures that are too high or too low. If the suction temperature is too low, it means that the refrigerant is not completely evaporated in the evaporator, which reduces the heat exchange efficiency of the evaporator, and the suction of the wet steam will form a compressor liquid hammer. The inspiratory temperature should be 5 to 10higher than the evaporation temperature under normal conditions.

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


5. The refrigeration system with liquid start:


1) Foaming with liquid start can be clearly observed on the oil sight glass. The root cause is that a large amount of refrigerant dissolved in the lubricating oil and sinking under the lubricating oil suddenly boils when the pressure suddenly drops, and causes the foaming phenomenon of the lubricating oil, which easily causes liquid shock.

2) The compressor is equipped with a crankcase heater (heater) to prevent refrigerant migration. Shut down for a short time to maintain the crankcase heater energized. After a long period of downtime, heat the oil for several or ten hours before starting the machine. The installation of a gas-liquid separator on the return line can increase the resistance of refrigerant migration and reduce the amount of migration.


6. The refrigeration system appears to return oil:


1) Lack of oil can cause serious lubrication shortage. The root cause of lack of oil is not how much and how slow the compressor is, but the system is not good. The oil separator can be installed to quickly return oil and extend the compressor's return-free operation time.

2) When the compressor is higher than the evaporator, there is no oil return bend on the vertical return pipe. The oil return bend should be as compact as possible to reduce oil deposits. The spacing between the oil return bends should be appropriate. When the number of oil return bends is relatively large, some lubricants should be added.

3) The compressor starts frequently. The frequent start of the compressor is not conducive to oil return. Since the continuous operation time is short, the compressor stops, and the return air pipe does not have a stable high-speed air flow, and the lubricating oil can only remain in the pipeline. If the oil is less than the oil, the compressor will be short of oil. The shorter the running time, the longer the pipeline, the more complicated the system, and the more serious the oil return problem.


7. The refrigeration system evaporation temperature is low:


The evaporation temperature has a great influence on the cooling efficiency. For every 1 degree reduction, the same cooling capacity is required to increase the power by 4%. Therefore, when the conditions permit, it is advantageous to increase the evaporation temperature appropriately, and the evaporation temperature is generally 5 to 10 degrees lower than the outlet temperature.

Although the evaporation temperature can be reduced by cooling, the cooling capacity of the compressor is reduced, so the cooling speed is not necessarily fast. Moreover, the lower the evaporation temperature, the lower the refrigeration coefficient, the higher the load, the longer the running time, and the higher the power consumption.


8. The exhaust refrigeration system is overheating:


The main reasons for exhaust super heat are as follows: high return air temperature, motor heating, high compression ratio, reverse expansion and gas mixing, compression temperature rise, refrigerant type, and high condensing pressure.

Regarding the specific reasons and analysis of the exhaust system overheating in the refrigeration system, we have published an article in the refrigeration encyclopedia before specifically, and interested friends can view the previously published articles.


9. The refrigeration system has a low intake temperature:


1) The expansion valve opening degree is too large. Because the temperature sensing element is loosely tied, the contact area with the return air pipe is small, or the temperature sensing element is not wrapped with the heat insulating material and the wrapping position is wrong, the temperature measured by the temperature sensing element is inaccurate, close to the ambient temperature, and the expansion valve is operated. The degree of opening increases, resulting in too much liquid supply.

2) The refrigerant charge is too much. The refrigerant charge is too much, occupying a part of the volume inside the condenser, so that the condensing pressure is increased, and the liquid entering the evaporator is increased. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked by the compressor contains liquid droplets. Thus, the temperature of the return air duct drops, but the evaporating temperature does not change because the pressure does not decrease, and the degree of super heat decreases. Even if the small expansion valve is closed, there is no significant improvement.


10. Refrigeration system lack of fluorine:


1) When the amount of fluorine is small or the regulating pressure is low (or partially blocked), the valve cover (corrugated pipe) of the expansion valve and even the inlet port will be frosted; when the amount of fluorine is too small or substantially no fluorine, the appearance of the expansion valve No reaction, only a little sound of the airflow can be heard.

2) To see which end of the ice from the beginning, is from the liquid separation head or from the press back to the gas tube, if the liquid separation head is the lack of fluorine, from the press is more fluorine.



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