Abstract: The air supplied to a fuel cell module is pumped with a compressor that has a moisturizing function in order to provide sufficiently moisturized oxidant. The compressor operates at very low pressure and the moisturization corresponds approximately to the dew point at the cooling water outlet temperature. If adequate moisturizing of the oxidant is no longer occurring at the defined low pressure, the input pressure is increased and the oxidant output is choked in a regulated manner. A corresponding fuel cell assembly with a polymer electrolyte membrane, i.e., a PEM fuel cell system includes the corresponding pump compressor and a controlled throttle valve at the exit side.