Stiffening beam for the passenger compartment of a motor vehicle for supporting an air distribution box of a climate control installation.

The beam has a body extending longitudinally along a constant direction and including windows (8, 9) at its ends for longitudinal introduction of selective air distribution units inside the beam. The body includes end fittings (12, 13) for reinforcing and fixing the beam to a passenger compartment of a vehicle. The fittings cover a zone of the beam comprising openings. An independent claim is also included for a process for assembling a beam with units for selectively distributing air.