A fan having an air guide and a flywheel is provided, the flywheel being attached to a shaft, for cooling an electric motor. The electric motor has a rotor which can be attached to the shaft. The air guide is arranged in an interchangeable manner at a position between the flywheel and the rotor with respect to the axial direction, and has an air guide opening with an inner cross section for the purpose of forming a blowing channel. An air flow generated by the flywheel can be guided through the blowing channel in the axial direction. The inner cross section is smaller than an outer cross section of the rotor.