Figure 1: The maintenance worker is changing the compressor in the fridge.
As we have mentioned in the first part, it’s the refrigeration capacity, the clean piping system, and the drying filter that deserve our attention. In addition, this article will give other three aspects, including quick replacement of compressor, nitrogen protection, and refrigerant quality.
You should replace the compressor as quickly as possible. Once the refrigeration pipe is opened, the air will enter the system, and the water in the air is easy to cause the refrigerant to unstable or ice jam, especially in the R134a refrigerant. When pulling out the rubber plug of the connecting pipe of the new compressor, if you can hear the sound of airflow and gas ejection, it means that the compressor has no leakage.
Once you remove the rubber plug, you should weld the compressor's three pipes to the condenser, evaporator, and service pipe as soon as possible to avoid exposure for a long time. Otherwise, it will cause the vinegar oil inside the R134a refrigerant to dissolve with air and water, leading to an unstable system, especially on rainy days. The R600 refrigerant uses mineral oil which is not as absorbent as vinegar oil, but you should also take it carefully.
A Xingnan BD / BG-313 refrigerator, using R134a refrigerant. The refrigeration effect of the new compressor is poor.
Figure 2: Xingnan refrigerator.
Analysis and Maintenance
When it’s powered, the sound of the refrigerant flow is not constant, and the pointer of the low-pressure gauge connected to the service pipe is unstable. It has been swinging up and down to a certain extent. We estimated that it’s the maintainer left the compressor pipe or system opening so long that there was air in the pipe, and then the vacuum time was short.
After releasing the refrigerant, you should vacuum it again, and use gas welding to heat the dry filter shell to facilitate the evaporation of water absorbed by the molecular sieve.
As it is unilateral pumping, you must pump out the gas on the high-pressure side through tiny capillaries. Therefore, the low-pressure gauge shows that it has reached -1ate in a short time, which is not true. The vacuum degree on the high-pressure side is not reached, so the vacuum time should be more than 30 minutes. Of course, pumping from both sides (high- and low-pressure side) is better in effects and efficiency.
According to the filling amount specified on the nameplate, you should accurately fill the device. The refrigerant sounds like continuously running water, and the range of pointer of the low-pressure gauge is stable, so the refrigeration effect is normal.
In the rainy season or relative humidity of the environment, replacing the compressor requires more rapid operation to avoid wet air into the system, as well as appropriately extended vacuum time.
In the process of replacing the compressor, inexperienced maintenance workers took so long to weld the orifice and caused extremely high welding temperature, resulting in a large number of oxides in the system.
The refrigerant flowing through the system is easy to block the filter, capillary, and other devices, and even the small oxides flee to the cylinder of the piston compressor against the high-pressure valve (plate), causing the high-pressure valve plate not to tight sealing, and weak exhaust.
Therefore, if possible, you’d better add nitrogen to protect the welding, so it could reduce the oxides because of high-temperature welding.
You should use a double-nozzle filter, connecting one nozzle with the condenser, and the other with nitrogen. Generally, nitrogen pressure is about 0.02MPa. Feel the air outlet by your hand and you would feel a trace of gas flow out. If nitrogen flow is large, it’s not good for welding, and small flow is easy to produce oxides, reducing the significance of adding nitrogen.
Figure 3: A double-nozzle drying filter for the fridge and refrigerator.
For a Galanz BCD-210N fridge, the worker has replaced two compressors of the same brand and specification continuously. The compressors were both weak for exhaust after less than two months.
Analysis and Maintenance
After cutting the filter, the maintenance worker found that there were a lot of oxides inside, which caused the extremely high pressure of the compressor for a long time, and the extremely low pressure. The compressor exhaust valve plate was aging, the seal was not strict, and the high and low pressure gas leaked. In addition, the fine oxides are also easy to enter the exhaust valve plate.
Flush the refrigeration system again. You should replace the single-nozzle filter with a double-nozzle drying filter, and add 0.02MPa nitrogen into one of the nozzles. Then you could weld the exhaust pipe, capillary, and suction pipe orifice of the compressor. Nitrogen protection welding can effectively reduce the production of oxides and improve the performance and service life of the compressor.
The nitrogen pressure should be 0.02Mpa - 0.03Mpa. Extremely high pressure will cause welding difficulties, and extremely small pressure will fail to protect the welding.
Before replacing the compressor, you should clearly know the refrigerant type. R134a and R600a refrigerant should not be used at the same time. The R134a refrigerant uses vinegar oil, whose refrigerant filling volume is generally about 200g (according to the capacity of the fridge), while the R600a type uses mineral oil.
And because of the large cooling capacity of the unit of R600a refrigerant, the refrigerant filling volume is relatively small. Generally, the filling volume is about 50g in the fridge (determined by the capacity of the fridge).
If you have confused the two refrigerant filling volumes, it still cools it but with bad effects, even leading to danger. The capillary of R134a refrigerant is about 15% longer than that of R600a. R600a refrigerant is flammable, so the internal electrical lines and joints of the compressor are more stringent than the R134a refrigerant.
The R134a refrigerant operates with positive pressure on the low side, while the R600a operates with negative pressure on the low side. When filling refrigerant, please pay attention to the R134a and R600a marks on the nameplate.
In addition, it’s necessary to choose the correct refrigerant brands. The well-known enterprises could well guarantee refrigerant purity, water content. Some cheap refrigerants may result in bad cooling effects, high pressure, and even ice blocking. Therefore, you’d better choose the noted manufacturers of refrigerants.
The compressor of a Midea BCD-241WM double-door refrigerator using R600a refrigerant was damaged. After replacing the compressor and filling the refrigerant, the maintenance worker found that the refrigeration effect was bad.
Figure 4: R600a refrigerant.
Analysis and Maintenance
The maintenance man has changed the compressor according to the requirements of the refrigerator maintenance specification process. But there were still faults. Then the worker used the R600a refrigerant, and the refrigeration effect was improved much. After an hour, the ice box reached -16℃ (no load in the cabinet), and the freezer box reached -5℃, which have achieved the expected set temperature.
Through the low-pressure gauge of the service pipe, the worker found that it was in a state of negative pressure. By measuring the compressor running current, it has reached the current value of the nameplate.
After two hours, the pressure gauge at the low-pressure side still showed 0.03MPa due to the bad quality of the refrigerant. According to the characteristics of refrigerants, if the refrigeration cycle was stable, the pressure at the low-pressure side should be negative. We figured that it’s because the refrigerant was overcharged. After discharging some, we found that the refrigeration effect was worse.
And then we suspected that there were faults with the vacuum. So we re-discharged the refrigerant and pumped the compressor out for one hour. The machine was finally normal.
The quality of refrigerant determines whether the refrigeration system could operate normally, effectively, and stably. You are suggested to choose the refrigerant from the manufacturers with reputation. Besides, you’d better use a quantitative filling machine for accurate filling to avoid the trouble of gauge pressure estimation and improve maintenance efficiency!