*In the field, it is hard to find out how much oil is circulating with the refrigerant. It helps to know the complete history of the equipment. On larger equipment, you can observe the oil level in the crankcase and/or reservoir. However, if oil has been added, the crankcase level may not indicate the correct oil charge.
Oil separators, such as the one illustrated here, can effectively remove oil from refrigerated vapors. The oil removed usually collects at the bottom of the separator. From there, it is returned periodically to the crankcase via the reservoir. The relationships of solubility, pressure, and temperature between oil and refrigerant in the crankcase also apply here.
*Excerpt from Technical Institute Manual One of the Refrigeration Service Engineers Society.
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