Temperature and hydration management are very important points for operating fuel cell systems and for optimizing their energy balance. In this paper, the design and the manufacture of an air conditioning device dedicated to proton exchange membrane (PEM) fuel cells are presented. Experimental thermal behavior laws are described and are intended to be integrated in a fuel cell powertrain model to drive the fuel cell without using an expensive and not adapted hygrometry measurement system. Experiments on a low power-testing bench (500 W) have been carried out, showing the efficiency of the system. Fuel cell polarization curves are shown, overheating and thermal inertia durations are also provided and taken into account for optimizing the regulation. (c) 2005 Elsevier B.V. All rights reserved.