How to Replace Refrigerator Compressor

Figure 1: LG refrigerator compressor.

A compressor is a machine that compresses gas and increases the pressure of the gas at the same time. It is widely used, and common application fields include: HVAC, refrigeration cycle, silicon chemical industry, petrochemical industry, natural gas transportation, etc.

If the refrigerator compressor shows the following signs during use, it means that the compressor needs to be replaced.

1. Signs of a Damaged Refrigerator Compressor

1. The compressor is running normally but not cooling.

2. Compressor cooling is normal, but there is a "bang" metal collision sound. If the compressor sounds abnormal, such as a "humming" sound, it indicates that there is something wrong inside the compressor.

After confirming that the refrigerator compressor is damaged, if you need to replace the compressor, you need to choose a new compressor with the same power as the original one, and a brand-name brand with good quality. It is best not to use second-hand or repaired compressors from unknown sources.

Compressor replacement is a highly professional operation and requires special tools, so it is best to ask professionals to replace it.

2. Detailed Steps to Replace Refrigerator Compressor

2.1 Remove the Old Compressor

1. First cut off the power of the refrigerator and remove the back cover of the refrigerator.

Figure 2: The back cover of the refrigerator.

2. Turn on the power again and check the status of the compressor again, and pay attention to whether the throttling device and filter are blocked, so as to determine whether it is necessary to replace them together, especially the filter drier.

Figure 3: Refrigerator filter drier.

3. After confirming that the compressor is broken, prepare to discharge refrigerant.
Cut the process tube open on the original compressor and discharge the refrigerant in the refrigerator. In order to prevent the refrigeration oil from rushing out, first file a slit at the lower part of the process tube end, and slowly discharge the refrigerant.

Pay attention to the ventilation of the working environment, and the speed of releasing the refrigerant should not be too fast, so as to avoid personnel being frostbitten by the refrigerant and the refrigeration oil in the compressor being released with the refrigerant. Once the compressor is in good condition after follow-up inspection, the lack of refrigeration oil will affect its normal use.

Note the color of the discharged refrigerant. If it is white or colorless, the internal cleanliness of the system is relatively high, and the compressor may not be damaged.

Figure 4: A technician is cutting the process tube.

4. When removing suction and exhaust pipes of the old compressor, make sure that the refrigerant has been exhausted. Fill the system with nitrogen, and ignite the welding gun. Use a welding gun to burn the welding points between the high-pressure exhaust pipe and the condenser, and these between the low-pressure suction pipe and the return air pipe.
Nitrogen filling operation is to avoid oxide inside the system, and pay attention to whether there are impurities and foreign materials on the inner wall of the copper pipe.

If the compressor oil is black or contains more impurities, clean the system, and replace the liquid storage tank and filter.
Fill cleaning fluid into the condenser and evaporator, then blow in high-pressure air or nitrogen. Repeat the above process two or three times, until the liquid blown out is clean. Then blow in high-pressure air or nitrogen from the opposite direction for more than 10 seconds.

Figure 5: Compressor discharge and return ports.

Notice:
①The cleaning fluid is required to be easily volatile.
②It is recommended to use R11.
③ It is necessary to ensure the cleanliness of the pipe orifice at the welding place.

5. Then unscrew the four foot fixing screws of the compressor, and remove the compressor.

Notice:
① If the compressor is burnt out, find out the cause of the compressor burnout. Otherwise, the compressor will burn out again.
②The high-pressure pipe of the refrigerator compressor must be cut with a cutter, and must not be welded off directly with a welding torch. Failure to do so creates the risk of fire and explosion.
③ If the damage of the refrigerator compressor is caused by internal leakage, it must be dealt with before replacing the compressor.

2.2 Install the New Compressor

First check whether the anti-shock rubber removed from the old compressor is aged or deformed. If it can be used, continue to use it. If it cannot be used, replace it with a new one, and then fix the new compressor on the base of the refrigerator.

Remove the sealing rubbers of the process tube, exhaust pipe and suction pipe of the new compressor (some are sealed by silver brazing, and the ends can be cut off) to release the hydrogen inside. And remove the rust layer of the three pipe orifices, and install a process shut-off valve at one end of the process pipe.

Clean up the ports to be welded on the condenser and the return air pipe. Use silver welding or brazing to connect the high-pressure exhaust pipe with the condenser, and the low-pressure suction pipe with the return air pipe.

Figure 6: A new refrigerator compressor.

2.3 Leak Detection

After welding, it is necessary to check the sealing of the welded place. First fill the refrigeration system with a certain pressure of dry hydrogen through the process shut-off valve. The pressure requirement is about 686-882Kpa. Wipe the welding points with soapy water to check for leaks. After confirming that the sealing performance is intact, dry and evacuate the system, and add refrigerant.

2.4 Evacuate the Compressor

Select different vacuum pumps according to the size of the system and the length of the piping. If a small vacuum pump is used to pump a large system, the evacuation time should be extended accordingly. When the negative value of the connected pressure gauge is not obvious, the evacuation time should be determined, and the pressure gauge is only used as an auxiliary judgment basis.

Figure 7: Connection diagram of refrigeration system evacuation (single side).

2.5 Add Refrigerant

When adding refrigerant, disconnect the connection between the yellow pipe and the vacuum pump, and then connect it to the refrigerant bottle and tighten it. The pressure method and the observation method are used when adding refrigerators.

Pressure method: Fill the evacuated refrigerator with a small flow rate of liquid refrigerant to 0.3MPa by combined meter valve at the process port, and wait for 5 minutes. After energizing the compressor to run for 15 minutes, adjust the working pressure of the process tube (called low pressure).

First observe the low pressure. If it is lower than 0.06MPa, add gaseous refrigerant (or a liquid with a small flow rate) from the process tube. With the extension of time (cooling of the freezer), the pressure will drop, and then add refrigerant. In this process, the pressure should be limited to not less than 0.08MPa.

Be patient during the adjustment process because the adjustment once or twice is inaccurate. If the pressure is high, directly discharge it from the meter valve (higher than atmospheric pressure), so there is no need to worry about air mixing.

Figure 8: Connect the yellow pipe to the refrigerant bottle.

2.6 Operate the Compressor

When the refrigerant is added to a certain amount, run the compressor and continue to add refrigerant to the specified pressure according to the pressure gauge. Refrigerant filling is generally carried out according to low pressure, and the low pressure of general models refers to the empirical value 0.4-0.6MPa set by the factory.

3. Confirmation Items after Compressor Replacement

Diagnose and eliminate the main cause of compressor failure to prevent recurrence.

3.1 Diagnostic Points

1. Confirm whether each welding point leaks.
The motor of the compressor is cooled by the refrigerant. If it runs without refrigerant, the overheating of the motor coil will cause burnout.

2. Confirm the operating pressure.
If air and moisture are mixed into the system, the system will freeze and the refrigerant will not flow. In addition, moisture will enter the compressor and cause mechanical failure.

3. Confirm the power supply voltage.
Confirm there is no phase-to-phase imbalance within the rated voltage ±10%.

4. Whether there is any dirt.
Dirty evaporators and condensers prevent heat exchange, resulting in high pressure rise and possible liquid compression. That is, the refrigerant does not completely evaporate, and when it returns to the suction side in a liquid state, it may enter the cylinder and cause liquid compression.

5. Confirm whether it is overloaded.
When the refrigerant is not easy to return to the suction side due to lack of refrigerant or blockage, the compressor will be overloaded, resulting in compressor failure.

6. The compressor cannot be placed horizontally or upside down.
Pay attention to keep the system clean: the interval between unplugging the rubber plugs of the compressor pipes and welding the piping should not exceed 10 minutes. During the transportation process, the inclination angle of the compressor shall not exceed 45 degrees, and the inclination angle of the installation shall not exceed 5 degrees.

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