Purpose — It is important to maintain the proper oil level in the compressor to ensure proper lubrication. This is necessary to avoid possible mechanical problems that can shorten compressor life. Maintaining the proper oil level also prevents excessive amounts of oil from being circulated through the system.

Oil charging is done to replace oil lost in a compressor as a result of a leak. It is also done whenever all the oil must be replaced in a compressor, such as when performing the cleanup o f a system that is contaminated as a result of a severe electrical burnout. Oil is removed from a compressor when it has been overcharged with oil, or when all the oil must be drained from the compressor to accomplish a service task.

Refrigerant oil usually comes in one-gallon or five-gallon containers. It is free of moisture, but readily absorbs moisture if exposed to air. Therefore, refrigerant oil should be bought in containers no larger than needed for the job. Do not use oil from a container that has been open for any significant length of time or that contains used oil. Never buy oil in bulk or in unsealed containers. Polyolester (POE) oil quickly absorbs moisture from the air which can contaminate the oil. Follow the manufacturer’s instructions when handling POE oil.

Before charging oil into a compressor, always refer to the manufacturer’s instructions for the equipment being serviced. Make sure to use the correct type of oil and the amount specified by the manufacturer.

Typically, welded hermetic compressors have no method of determining the oil level. Since these compressors are usually factory installed in assembled equipment, they are shipped with a full oil charge that is adequate for normal operation. The same is true for welded hermetic replacement compressors. Normally, there are no problems with the oil level in welded hermetic compressors, except in the case of an oil leak. In this case, the compressor is usually removed and the remaining oil drained from, the compressor’s suction stub or process tube. The correct amount of new oil is then charged into the compressor.

Semi-hermetic compressors, found in some commercial equipment, normally have an oil fill plug and oil level sightglass (Figure SP-6-2). This allows the oil level to be monitored.

A n oil level should always be observed in the oil sightglass, regardless of whether the unit is running or idle. When the compressor is running, the oil level is typically between 1/8 and 3/8 up from the bottom of the sightglass. Most semi-hermetic compressors also have an oil drain plug.

There are many ways to charge oil into a semi-hermetic compressor. The procedure in this section describes the use of a refrigeration oil pump to charge a semi-hermetic compressor using a closed system method.

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