A detailed mathematical model of vapor compression heat pumps is described. Model equations of the various heat pump components are given. The component models include the condenser, evaporator, accumulator, expansion device, and compressor. A brief discussion of the modeling techniques is presented, as is the solution methodology. Preliminary simulation results are also illustrated. The model developed predicts the spatial values of temperature and enthalpy as functions of time for the two heat exchangers. The temperatures and enthalpies in the accumulator, compressor, and expansion device are modeled in lumped-parameter fashion. Pressure responses are determined by using continuity-satisfying models for both the condenser and evaporator. The summary provides a list of future work anticipated in the area of dynamic heat pump modeling.