Before removing the dashboard the air distribution must be set manually to "footwell" in order to close the upper flaps of the air conditioner housing.
With air distribution "Center level open" the side air vent flap projects upwards out of the air conditioner housing. If the dashboard is removed in this condition, the side air vent flap can be unhooked in the process. If the side air vent flap is unhooked, the air volume in "DEF" position at the side air vent is not reduced