An evaporator's time-constant (t(c)) equation has been developed as part of a mathematical model describing the time-dependent behaviour of a refrigeration system. The magnitudes of the evaporator's t(c) were approximately 2 and 5 s, respectively for 100 and 50% loads imposed on the refrigerator. As a result of a step change in the inlet's water-temperature, the magnitudes of both t(c) and the two-phase heat-transfer coefficient (f(tp)) for the refrigerant system were altered. Although a step decrease in the inlet-water's temperature led to large increase in t(c), the system's behaviour stabilized quickly because f(tp) had also increased significantly. The predictions of this investigation showed that such an analysis is highly sensitive to the accuracy of the equations used to calculate both t(c) and f(tp) and this makes the experimental verification of this model desirable.