Abstract: Parallel connected compressors are provided with an oil management scheme in which an oil equalization port on one compressor is connected via an oil return solenoid operated valve within a small diameter line to an injection port of a second compressor, and vice versa. When the oil level in one compressor drops to a level sensed by an oil float switch, the oil float switch changes state, the oil return solenoid operated valve is opened, feeding its injection port and energizing a one minute on delay timer. Failure of the oil float switch to reset itself causes the compressor to go off on oil failure, and the oil return solenoid operated valve is closed. If the oil float switch resets itself at any time during the first minute, upon resetting, an off delay timer is energized to keep the oil return solenoid operated valve open for an additional minute, and the compressor continues to operate.

Abstract: A heat exchanger formed by concentric, spaced tubes defining a substantially annular chamber therebetween. There is an internal metallic fin comprising a strip of corrugated sheet metal extending spirally within the annular chamber with the adjacent turns of the spirally formed strip being spaced from each other to provide a spiral passageway between the side edges of adjacent turns. The metallic fin corrugated sheet metal strip bears a plurality of small apertures to significantly improve the boiling heat transfer coefficient.