Absorption heat pump technology may be improved by new cycle configurations by new working fluids. In this study, the effect of hypothetical working fluids on performance improvement is explored. The performance of two cycles is studied using three fluid property sources for ammonia/water, i.e., curve-fit experimental data, an ideal solution model, and the Peng-Robinson equation of stare model. The models require only minimal fundamental thermodynamic property, data for the two pure components, This allows investigation into the influence of each fundamental property on cycle performance, providing insight into desirable properties for new absorption fluid pairs. Variations of fundamental fluid properties are used as input to the models, showing that the volatilities of the refrigerant and absorbent have the greatest effect on cycle performance.