The oil tap is installed on a semi-hermetic compressor for the changing of oil and testing procedures. The internal pressure helps discharge the oil from the crankcase and acid tests can be made while the compressor is running. It allows the addition by vacuum or removal by pressure of oil while compressor is running. Detect hazardous refrigerant pooling in the crankcase before startup and control the removal using a compound gauge. The oil tap can be permanently installed.