Ten common causes of failure in refrigeration systems
a, liquid back
1. 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 superheat 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 may be returned.
2. For a small refrigeration system using a capillary tube, the amount of liquid added 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 backflow.
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.
b, with liquid start
1. The phenomenon that the lubricating oil in the compressor violently foams is called starting with liquid. The blistering phenomenon 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 is liable to cause liquid shock.
2. The compressor is equipped with a crankcase heater (electric 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.
c, return oil
1. When the compressor is at a higher position than the evaporator, the oil return bend on the vertical return pipe is necessary. 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.
2. Frequent starting of the compressor is not conducive to oil return. Since the compressor is stopped for a short running time, and the return air pipe does not have a stable high-speed airflow, 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.
3, lack of oil will cause serious lubrication shortage, the root cause of lack of oil is not how much and how slow the compressor is running, 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.
d, evaporation temperature
The temperature of the heat has a great influence on the cooling efficiency. For every 1 degree of reduction, the same amount of cooling is required to increase the power by 4%. Therefore, if the conditions permit, it is advantageous to increase the evaporation temperature appropriately to improve the cooling efficiency of the air conditioner.
The evaporating temperature of the household air conditioner is generally 5 to 10 degrees lower than the temperature of the air outlet, and during normal operation, the evaporating temperature is 5 to 12 degrees, and the outlet temperature is 10 to 20 degrees.
Although the evaporation temperature can be reduced at once, the cooling temperature can be reduced, but 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 operation time, and the higher the power consumption.
e, the exhaust temperature is too high
The reasons for the excessive exhaust gas temperature are as follows: high return air temperature, large motor heating, high compression ratio, high condensing pressure, refrigerant adiabatic index, and improper refrigerant selection.
f, liquid blow
1. 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 superheat.
2. Avoid inhaling temperatures that are too high or too low. Excessively high inspiratory temperatures, ie excessive superheat, will cause the compressor discharge temperature to rise. 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 suction temperature should be 5 to 10 ° C higher than the evaporation temperature under normal conditions.
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 from which end of the icing, 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.
h, low inspiratory temperature
1. The refrigerant charge is too much, which occupies part of the volume inside the condenser and increases the condensing pressure. The liquid entering the evaporator increases. 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 fall, and the degree of superheat decreases. Even if the small expansion valve is closed, there is no significant improvement.
2. 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.
i, high inspiratory temperature
1. 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 superheat is large, and the intake temperature is high.
2. The expansion valve port is clogged, the supply of liquid 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 temperature is increased.
3. Other reasons cause the inspiratory temperature to be too high. If the return air pipe is not well insulated or the pipe is too long, the inhalation temperature may be too high. Under normal circumstances, the cylinder head of the compressor should be half cold and half hot.
j, the exhaust temperature is too low
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. The reasons are:
1. The expansion valve is blocked by ice or dirty, and the filter is blocked, which will inevitably reduce the suction and exhaust pressures;
Insufficient refrigerant charge;
2. The expansion valve hole is blocked, the liquid supply is reduced or even stopped, and the suction and exhaust pressures are reduced.