In the calculation of heat exchangers, although there are rules of general trends related to the construction of the heat exchanger configuration and thermophysical properties, it is necessary to analyze each situation individually.

In the particular case of heat exchangers with phase change, such as direct expansion, condensation and pump evaporator, the program UNILAB COILS makes a correction of the benefits related to pressudre drops of the refrigerant.

In this mode, the iterative calculation can, in some situations, lead to a stall situation in the process of convergence due precisely to the application of this fix.

The only way to remedy this situation is to vary the number of circuits of the coil set in the calculation.