Compressor refrigeration oil plays a crucial role in lubrication, cooling, sealing, and noise reduction. Aging, water ingress, and carbonization of the oil can cause compressor wear, reduced refrigeration efficiency, and in severe cases, even motor burnout. When changing refrigeration oil, it is essential to use a dedicated refrigeration oil compatible with the refrigerant; ordinary machine oil must not be mixed. The complete procedure to change the refrigeration oil is described below and is important for system longevity.
Before replacement, disconnect the main power supply to the equipment, close the high and low pressure valves, and recover the refrigerant from the system. Turn on the compressor and pump the remaining refrigerant back to the condenser. Only proceed with disassembly after confirming that the system is pressure-free. Never drain oil under pressure to prevent refrigerant spray and frostbite. Allow the compressor to cool down for 1-2 hours until the unit temperature drops to room temperature before draining the oil. Draining oil at high temperatures can cause burns and splattering. While you change the refrigeration oil, always follow these safety steps carefully.
1. Drain the old oil
Locate the drain plug at the bottom of the compressor, place an oil collection container underneath, and slowly unscrew the drain plug to allow the old refrigerant oil to flow out naturally. Observe the color of the old oil. If the oil is black, cloudy, has a burnt smell, or contains impurities and moisture, it indicates that the system has carbonized internally. In addition to changing the oil, the piping should be cleaned and the filter drier replaced. After draining the old oil, briefly run the compressor for a few seconds to fling out any remaining waste oil in the crankcase, then drain the oil again. So, to change the refrigeration oil effectively, a thorough cleaning and inspection should be completed during this step.
2. Add new refrigeration oil
First, check the compressor nameplate to confirm the refrigeration oil type and the required amount.
There are two ways to add oil. One is to add it directly from the filler neck. Open the filler plug and slowly pour in the new oil using a funnel, constantly observing the oil level gauge. Control the oil level between 1/2 and 2/3 of the gauge.
Do not add too much oil, as this can cause liquid slugging and oil leakage; if the oil level is too low, there will be insufficient lubrication, causing wear on the bearings.
The second method is negative pressure filling. Close the exhaust valve and use the internal negative pressure of the compressor to draw the refrigeration oil into the crankcase. This method is suitable for semi-hermetic, reciprocating cold storage compressors.
Thus, it is important to know how to change the refrigeration oil according to equipment specifications.
3. Sealing and Vacuuming.
After refueling, tighten the drain plug and filler cap, and restore all pipe connections. Vacuum the refrigeration system for at least 30 minutes to completely remove any air and moisture introduced during the refueling process, preventing the refrigerant oil from acidifying and corroding the components. Once the operator achieves the vacuum, they refuel the system. In summary, when you change the refrigeration oil, proper vacuuming is essential for system health.
4. Testing and Operation
Power on the unit and let the compressor run unloaded for 10-20 minutes, continuously observing the oil level gauge for a rapid drop, checking the oil pressure for any abnormal noises from the compressor. After running for half an hour, recheck the oil level. If the oil level has dropped, add refrigerant oil as needed. Finally, record the oil change, noting the oil type, amount added, and date of replacement.
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