At the beginning of this study there existed at our laboratory a large mass of secondary refrigerant calorimeter data from testing various compressor and refrigerant combinations under ARI test conditions (5). Results from tests which had been run at various evaporating temperatures with a constant temperatare at the evaporator outlet and from tests where the evaporator temperature varied but tbe superheat was held at a constant 25F were plotted as shown by the solid lines in Fig. I and 2. Calculated capacity increases with superheat as a percent of constant superheat capacities using refrigerant thermodynamic properties only are shown as dotted lines. It is immediately apparent that superheat has a much greater effect on compressor performance than indicated by calculation.

Coneideratlon of the various causes for this anomalous behavior, including the literature review, led to a decision to study three possible causes.

1. Wet suction vapor at low superheat levels;
2. Refrigerant coming from solution in the oil in the compressor cylinders;
3. Internal suction vapor heating.