This work presents an experimental study of an important component of an ammonia-water absorption refrigeration cycle based on the falling film technology - the distiller, which is formed by two parts: the generator and the rectifier. It was carried out a parametrical study on the operation of the distiller by testing several parameters. The experimental results showed that the distilled ammonia vapor concentration always degraded as rectifier, generator, and concentrated solution temperatures increased and improved as concentrated solution mass flow rates and concentrated solution concentrations increased. The highest distilled ammonia vapor concentration obtained was of 0.9974. Photographic documentation of flow pattern over the generator tube bundle was also obtained resulting in both jet column and sheet patterns. Finally, a Nusselt number correlation for the ammonia-water falling film over the generator tube bundle was proposed based on the experimental results and compared with other authors' correlations.