Pressure-enthalpy (P-H) and temperature-entropy (T-S) diagrams for refrigerant R-134a are used to demonstrate the ordinary vapor compression (OVC) cycle. You can vary the condenser pressure (high pressure) and the evaporator pressure (low pressure); the coefficient of performance (COP) is calculated for the cycle. The COP is the ratio of heat transferred (from the cold reservoir Q_c) to the work W required to compress the gas in the compressor; a high value is desirable. Selecting "cycle" from the drop-down menu shows the components of the cycle, and moving the mouse over the circled numbers 1–4 on the cycle view displays the phases present at those points.