refrigeration station

Figure 1: The refrigeration system at manufacturing factory.

The blockages in the refrigeration system include ice, dust, oil and welding blockage, etc. Do you know the reasons for these blocking phenomenons? This article will introduce the causes and solutions. First, these blockages are accompanied by some common failures.

* The common phenomenons

The condenser is not hot while the evaporator is not cool.
The compressor running current is smaller than normal.
A pressure gauge is connected to the bypass valve, indicating negative pressure.
The running of the outdoor unit is silent, and there is a liquid sound in the evaporator.

* Ice-Blocked

The frozen water in the refrigerant causes a blockage in the pipes. Under these circumstances, the refrigeration system is normal at the beginning. After a period of time, there is a blocking fault. After shutdown, the refrigeration will automatically recover, but the ice blocking will be repeated after the machine is started again.

* Dust Blockage

It is the rust debris and dirt that have blocked the pipes, generally in the capillary or filter. The fault is characterized by an extremely slow low-voltage balance which lasts more than 30 minutes.

* Oil Blockage

The cause is that the lubricating oil gets into the refrigerant and blocks the pipe. The fault often occurs in the capillary. If the 3-way meter is connected, and the pressure in the measuring system has been maintained at 0MPa (not negative), it would mean that the capillary or filter is under a “half blocked” state.

Ice Blockage

* Reasons

Impure refrigerant.
When dismantling the air conditioner, the stopping valve of the outdoor unit is not closed, so that the refrigerant is exposed to the wet environment for a long time.
Improper use.

If the water in the refrigerant is not much and the ice blockage is not serious, firstly you can release all the refrigerant. Then you should bake the evaporator and condenser with gas welding to dry the refrigeration system through the vacuum pump.

Stop vacuuming it after the water is drained. And then you should replace the filter, add nitrogen of 0.8Mpa from the low-pressure bypass valve, and check for the leaks on the chlorine welding joint of the filter with the detergent. After confirming that the pipeline does not leak, you can release the nitrogen, and then vacuum the system, add the fluorine to give a test run.

Keep in mind that you should not fill the refrigeration pipeline with methanol. Although methanol can lower the freezing point and be helpful for minor ice blockage, it will react with the refrigerant to generate hydrofluoric acid and hydrochloric acid to corrode pipes, causing the filter to blocked. The air conditioner using refrigerant filled with methanol would generally have failure after 6 months, including the compressor insulation reduction and the motor burnout.

In some cases, improper use will cause excessive water in the refrigeration system. For example, some users put the pipe connecting the indoor unit with the outdoor unit in the wet trench. If the low-pressure pipe is broken, it would gradually leak, resulting in negative pressure in the pipeline, which could suck the water into the refrigeration system.

When the user opens the nut of the low-pressure pipe, there would be water flowing out, indicating the air conditioner is damaged completely. To repair it, the maintenance worker should remove the whole pipeline. After welding the leaking point, the pipeline should be cleaned with ethanol to remove the water. Then clean the condenser and compressor thoroughly with the carbon tetrachloride and kerosene.

Dust Blockage

The key is to confirm the nature and cause of the fault. For example, when installing a Chunlan KFR-32GW split air conditioner, and excluding the air in the indoor unit, the worker found that there had been no refrigerant. After vacuuming it, the worker added F22 refrigerant and then started it with the remote control. When the pressure reaches 0.25MPa, the compressor was overheated, the overheating protector jumped, and the compressor stopped working.

At first, the user figured that there was air in the system. He discharged the refrigerant and vacuumed the compressor again, but the fault was not solved. The user has asked a few maintenance staff to check it. Some said that the compressor was short of oil, while others thought that it was a short circuit in the compressor coil. So they refueled, pumped, added fluorine, and even changed the compressor, but they can not troubleshoot.

In fact, the cause of the fault is that the valve of the air conditioner was not closed after disassembled. After a period of use, the air entered the pipeline causing corrosion, and the rust debris blocked the filter. Finally, the use replaced the filter and after a series of operations, the trouble was eliminated.

a filter used for the refrigeration system

Figure 2: A filter in the refrigeration system.

This example shows that a comprehensive analysis of the causes and consequences of the failure is essential.

Capillary Frosting

* Phenomenon

The air conditioner is not cooling, and there is frost on the capillary.

* Reasons

It is very similar to the failure phenomenon of the lack of fluorine, so you can try to add the F22 refrigerant. After that, if the frost disappears, the air conditioner should have lacked fluorine. But if there is still frost, the fault is a capillary blockage.

* Troubleshooting

To find the blockage point, you should cut off the capillary and insert a thin wire into both ends to dredge it. Pay attention to prevent the refrigerant from spraying, which splashing on the body will cause frostbite. After dredging the capillary, you could use a copper tube with an inner diameter equal to the outer longitude of the capillary to cover the outside, so that both ends of the capillary are tightly connected. And then you should weld both ends of the tube with silver. When welding, you must avoid making the solder flow into the capillary.

The second way is to replace the capillary with a new one of the same specifications after removing all the refrigerant in the pipeline. Before welding the new capillary, you should cut both two ends to a 35-degree bevel to allow the refrigerant to flow freely in it. When welding, the flame must be aligned with the welding joint. Once the copper tube is heated to red and white (up to about 700℃), the silver electrode should be quickly pointed. In this way, the welding joint will be uniform and smooth, and will not leak.

4-Way Valve Slider Blocked

When the 4-way valve of the air conditioner is powered on and off, the flow direction of the refrigerant changes accordingly, realizing the conversion between refrigeration and heating. Figure 3 shows the four-way valve structure, also showing its connection with the external pipeline, wherein the upper pipe is connected with the compressor exhaust pipe, the bottom of the middle pipe is connected with the compressor suction pipe. The right one is connected to the condenser inlet pipe, and the left one is connected to the evaporator outlet pipe.

4-way valve structure and movement

Figure 3: 4-way valve structure diagram.

The 4-way valve is a special part of the heat pump air conditioner. When the refrigerant has impurities or the carbide generated by the deterioration of the refrigerating oil will block the capillary, causing the nylon slider in the 4-way valve difficult to move, and the conversation between refrigeration and heating state cannot be achieved.

* Troubleshooting

First, you should use a power socket to connect the 220V AC to the outdoor unit. And then you should unplug the air conditioner power plug and the two terminal leads of the four-way valve, hold the insulation part of the lead wire, plug the lead end directly into the power socket to energize the four-way valve, and force the solenoid coil of the four-way valve to pull the slider. After it is repeated on and off 4 ~ 5 times, there is the sound, and it means that the slider can move normally.

During the maintenance, if it is difficult to introduce a 220V power supply, you can also use the power supply on the outdoor terminal. Start the air conditioner by the remote control, set the refrigeration state. 3 minutes later, the outdoor terminal has electricity, so you can use the terminal board 220V voltage directly on the four-way valve to give an adding electricity test.

If the 4-way valve is directly electrified, and the slider inside can not move, the maintenance personnel can abandon the 4-way valve after obtaining the consent of the user. You could use gas welding to weld 4 copper pipes above and below the lower four-way valve, connect the outlet pipe and the inlet pipe with two U-shaped pipes respectively, and connect the outlet pipe of the evaporator with the inlet pipe of the compressor.

After pressing, leak detection, pumping, fluorine filling, the air conditioner can be cooling. The pipeline changes would not affect the cooling capacity of the air conditioner but make the heating function lost. Therefore, this method is helpful to repair air conditioners of low value.

* Replace the four-way valve

four-way valve for refrigeration

Figure 4: A 4-way valve.

When the slider in the four-way valve is seriously deformed, you can only replace it. First, remove the four-way valve coil, and then weld the connecting pipes. Before welding, you should unload the solenoid coil, keep it under the horizontal state, and put the 4 pipes in place, ensuring the direction and angle are the same as the original.

You should use a neutral flame, wrap the four-way valve with a wet towel, and weld the upper high-pressure nozzle first. After the high-pressure pipe welding is completed and cooled down, the inlet pipe in the middle can be welded, and then the condenser inlet and evaporator outlet.

Since the pipe at the bottom side is difficult to weld, you must master the fire intensity. The method is to look at the welding joint, and weld it as soon as the fire touches it. You should weld more than half of the orifice, and quickly replace the wet towel wrapping the four-way valve, to prevent the extremely high temperature in the core, which would cause the nylon slider deformation. But the towel should not be much wet to prevent water from entering the cooling system through the unwelded orifice.

After welding the whole orifice, you must bake the welding joint immediately to ensure firm welding with no air leakage. The whole welding process should not exceed 15 minutes. Repeated welding will easily bake the nylon slider to deformed.

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