An equivalent-capacitance approach (ECA) was proposed to determine the performance of a heat exchanger with a change in the physical state of one of the working fluids. The new methodology was an alternative form of the popular log-mean-temperature-difference approach (LMTDA) which could avoid the often troublesome iterative computations involving natural logarithms. Sample simulations were made using both methods for a refrigerant condenser and an evaporator. It was found that whenever convergence was achieved, both methods gave very similar results. However, the iteration stability of the ECA was much better, especially when the heat transfer value (UA) of the heat exchanger was large. Consequently, the ECA was considered to be a better alternative to the LMTDA in determining the performance of a refrigerant coil.