How to Replace Refrigeration Oil in Compressors
1. Functions of Refrigeration Oil
Lubrication: It lubricates the surfaces of moving components in the compressor, reduces resistance and friction, lowers power consumption and extends service life.
Cooling: It timely removes heat generated by friction on moving surfaces to prevent excessive temperature rise or burnout of the compressor.
Sealing: Lubricating oil penetrates the sealing surfaces of friction parts to form an oil seal and prevent refrigerant leakage.
Noise reduction: The oil continuously flushes friction surfaces and carries away abrasive debris, reducing wear of moving parts.
2. Conditions for Refrigeration Oil Replacement
After long-term operation of the refrigeration unit, replace oil when the compressor runs for 2,000 hours for the first maintenance; subsequent oil change shall be carried out after cumulative operation of 10,000~12,000 hours.
If the compressor needs replacement due to motor burnout, the oil shall be changed after continuous operation for 100 hours post replacement.
For refrigeration units used in pipe coil warehouses, refrigeration oil must be replaced after 100 hours of operation.
Replace oil according to the cleanliness of refrigeration oil in the refrigeration system.
3. Operating Specifications for Refrigeration Oil Replacement
Make the crankcase communicate with atmosphere
Close the high-pressure discharge and low-pressure suction shut-off valves. Use the service valve needle on the compressor to release refrigerant inside the compressor, so that the crankcase communicates with the atmosphere.
Unscrew the oil drain plug at the bottom of the crankcase, completely drain the refrigeration oil inside the crankcase, remove and clean the filter screen.
Blow nitrogen through the low-pressure charging valve needle, block the oil outlet by hand to increase internal pressure of the unit, and further discharge residual oil inside. Dry the cleaned filter screen, install it back into the unit and tighten the oil drain plug.
Methods for injecting refrigeration oil into the crankcase
Unscrew the service port plug on the side of the compressor crankcase as the filling port, and pour refrigeration oil into the crankcase via suitable tools.
(For reciprocating compressors) Connect the low-pressure hose of the refrigerant manifold gauge to the low-pressure service valve needle of the compressor housing. Use a vacuum pump to evacuate the crankcase to negative pressure. Disconnect another refrigerant charging hose; insert one end into the container filled with refrigeration oil, and connect the other end to the valve needle at the low-pressure suction side of the oil pump. The negative pressure inside the crankcase will draw refrigeration oil into the crankcase.
Since a certain amount of residual oil may remain in the original system, less oil can be added during refilling, generally slightly above the lower limit mark on the oil sight glass.
After filling refrigeration oil, tighten the service plug or remove the charging hose, connect the refrigerant manifold gauge and evacuate the compressor.
Upon completion of evacuation, open the high and low-pressure shut-off valves of the compressor and check for refrigerant leakage.
If no leakage is found, wait for 20 minutes and start the unit.
Immediately check the compressor lubrication condition and oil level in the sight glass after startup. If the oil level is lower than the normal range (1/4 of the sight glass), refrigeration oil must be supplemented. If necessary, mount an oil pressure gauge on the oil pump valve needle to monitor oil pressure. The pressure at the suction side of the oil pump shall be basically consistent with the low-pressure suction pressure. The allowable oil pressure differential is 1.4~3.5 bar. Screw compressors adopt differential pressure oil return without oil pumps.
4. Precautions for Oil Filling
Refrigeration oil is hygroscopic. Water will chemically react with oil, and the mixture cannot be removed by vacuum pumping. Extra care shall be taken during operation to minimize air ingress into the system and oil storage container.
For compressor replacement: a certain amount of refrigeration oil is already stored in the original refrigeration system. Blow out the oil inside the system if necessary. If a large volume of oil remains in the system, liquid slugging risk exists upon startup.
It is recommended not to replace refrigeration oil on rainy days.
Lubrication: It lubricates the surfaces of moving components in the compressor, reduces resistance and friction, lowers power consumption and extends service life.
Cooling: It timely removes heat generated by friction on moving surfaces to prevent excessive temperature rise or burnout of the compressor.
Sealing: Lubricating oil penetrates the sealing surfaces of friction parts to form an oil seal and prevent refrigerant leakage.
Noise reduction: The oil continuously flushes friction surfaces and carries away abrasive debris, reducing wear of moving parts.
2. Conditions for Refrigeration Oil Replacement
After long-term operation of the refrigeration unit, replace oil when the compressor runs for 2,000 hours for the first maintenance; subsequent oil change shall be carried out after cumulative operation of 10,000~12,000 hours.
If the compressor needs replacement due to motor burnout, the oil shall be changed after continuous operation for 100 hours post replacement.
For refrigeration units used in pipe coil warehouses, refrigeration oil must be replaced after 100 hours of operation.
Replace oil according to the cleanliness of refrigeration oil in the refrigeration system.
3. Operating Specifications for Refrigeration Oil Replacement
Make the crankcase communicate with atmosphere
Close the high-pressure discharge and low-pressure suction shut-off valves. Use the service valve needle on the compressor to release refrigerant inside the compressor, so that the crankcase communicates with the atmosphere.
Unscrew the oil drain plug at the bottom of the crankcase, completely drain the refrigeration oil inside the crankcase, remove and clean the filter screen.
Blow nitrogen through the low-pressure charging valve needle, block the oil outlet by hand to increase internal pressure of the unit, and further discharge residual oil inside. Dry the cleaned filter screen, install it back into the unit and tighten the oil drain plug.
Methods for injecting refrigeration oil into the crankcase
Unscrew the service port plug on the side of the compressor crankcase as the filling port, and pour refrigeration oil into the crankcase via suitable tools.
(For reciprocating compressors) Connect the low-pressure hose of the refrigerant manifold gauge to the low-pressure service valve needle of the compressor housing. Use a vacuum pump to evacuate the crankcase to negative pressure. Disconnect another refrigerant charging hose; insert one end into the container filled with refrigeration oil, and connect the other end to the valve needle at the low-pressure suction side of the oil pump. The negative pressure inside the crankcase will draw refrigeration oil into the crankcase.
Since a certain amount of residual oil may remain in the original system, less oil can be added during refilling, generally slightly above the lower limit mark on the oil sight glass.
After filling refrigeration oil, tighten the service plug or remove the charging hose, connect the refrigerant manifold gauge and evacuate the compressor.
Upon completion of evacuation, open the high and low-pressure shut-off valves of the compressor and check for refrigerant leakage.
If no leakage is found, wait for 20 minutes and start the unit.
Immediately check the compressor lubrication condition and oil level in the sight glass after startup. If the oil level is lower than the normal range (1/4 of the sight glass), refrigeration oil must be supplemented. If necessary, mount an oil pressure gauge on the oil pump valve needle to monitor oil pressure. The pressure at the suction side of the oil pump shall be basically consistent with the low-pressure suction pressure. The allowable oil pressure differential is 1.4~3.5 bar. Screw compressors adopt differential pressure oil return without oil pumps.
4. Precautions for Oil Filling
Refrigeration oil is hygroscopic. Water will chemically react with oil, and the mixture cannot be removed by vacuum pumping. Extra care shall be taken during operation to minimize air ingress into the system and oil storage container.
For compressor replacement: a certain amount of refrigeration oil is already stored in the original refrigeration system. Blow out the oil inside the system if necessary. If a large volume of oil remains in the system, liquid slugging risk exists upon startup.
It is recommended not to replace refrigeration oil on rainy days.
