10 common maintenance faults of refrigeration equipment!

I. Liquid return:

1. For refrigeration systems using expansion valves, liquid return is closely related to improper selection and use of expansion valves. Excessive expansion valve selection, too small superheat setting, incorrect temperature sensor installation method or insulation wrapping damage, and expansion valve failure may all cause liquid return.

2. For small refrigeration systems using capillary tubes, excessive liquid addition will cause liquid return. When the evaporator is severely frosted or the fan fails, the heat transfer becomes poor, and the unevaporated liquid will cause liquid return. Frequent temperature fluctuations can also cause expansion valve reaction failure and cause liquid return

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

II. Liquid start:

1. The phenomenon of violent bubbling of the lubricating oil in the compressor is called liquid start. The bubbling phenomenon during 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 sunk under the lubricating oil suddenly boils when the pressure suddenly drops, causing the lubricating oil to foam, which can easily cause liquid hammer.

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

III. Oil return:

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

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

3. Lack of oil will cause serious lack of lubrication. The fundamental reason for lack of oil 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 extend the compressor's oil return-free operation time.

IV. Evaporation temperature:

The evaporation temperature has a great influence on the refrigeration efficiency. For every 1 degree it decreases, the power needs to increase by 4% to produce the same amount of cooling. Therefore, if conditions permit, it is beneficial to increase the evaporation temperature appropriately to improve the refrigeration efficiency of the air conditioner.

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

Although blindly lowering the evaporation temperature can reduce the temperature difference, the refrigeration capacity of the compressor is reduced, so the refrigeration speed is not necessarily fast. Moreover, the lower the evaporation temperature, the lower the refrigeration coefficient, while the load increases, the operation time is extended, and the power consumption will increase.

V. Exhaust temperature is too high

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

VI. Liquid hammer

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

2. Avoid too high or too low suction temperature. If the suction temperature is too high, that is, the superheat is too large, it will cause the compressor exhaust temperature to rise. If the suction temperature is too low, it means that the refrigerant is not completely evaporated in the evaporator, which not only reduces the heat exchange efficiency of the evaporator, but also causes compressor liquid hammer due to the inhalation of wet steam. Under normal circumstances, the suction temperature should be 5 to 10°C higher than the evaporation temperature.

VII. Fluorine addition

1. When the amount of fluorine is small or its regulating pressure is low (or partially blocked), the valve cover (bellows) of the expansion valve and even the liquid inlet will be frosted; when the amount of fluorine is too small or there is basically no fluorine, the surface of the expansion valve will not react, and only a slight sound of airflow can be heard.

2. See which end the icing starts from, whether it is from the liquid distributor or from the compressor return pipe. If it starts from the liquid distributor, it means there is a lack of fluorine, and if it starts from the compressor, it means there is too much fluorine.

VIII. Low suction temperature:

1. Too much refrigerant is charged, occupying part of the volume in the condenser and increasing the condensing pressure, and the amount of 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 pipe drops, but the evaporation temperature does not change because the pressure does not drop, and the superheat decreases. There is no significant improvement even if the expansion valve is closed.

2. The expansion valve is opened too much. Because the temperature sensing element is tied too loosely, the contact area with the return air pipe is small, or the temperature sensing element is not wrapped with insulation material and the wrapping position is wrong, the temperature measured by the temperature sensing element is inaccurate and close to the ambient temperature, which increases the opening degree of the expansion valve action and leads to excessive liquid supply.

IX. High suction temperature:

1. The refrigerant charge in the system is insufficient, or the expansion valve opening is too small, resulting in insufficient circulation of the system refrigerant, a small amount of refrigerant entering the evaporator, a large degree of superheat, and thus a high suction temperature.

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

3. Other reasons cause the suction temperature to be too high, such as poor insulation of the return air pipe or too long pipe, which can cause the suction temperature to be too high. Under normal circumstances, the compressor cylinder head should be half cool and half hot.

X. Exhaust temperature is too low

The exhaust pressure is too low. Although the phenomenon is manifested at the high-pressure end, the cause is mostly at the low-pressure end. The reasons are:

1. The expansion valve is blocked by ice or dirt, and the filter is blocked, which will inevitably cause the suction and exhaust pressures to drop; the refrigerant charge is insufficient;

2. 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.