(57) A holding system for holding an external unit of a fluid conditioning system (such as an air conditioning system), comprising an internal unit operatively connected via an elongate interconnector to the external unit in an roof opening of a sloping roof comprising an upper roof surface, said holding system comprising; a watertight base comprising a base circumference and an upper side, a watertight wall which extends upwardly from the upper side of the base, is connected to the base in a watertight manner and extends along part of the base circumference of the base to define a water outlet for the drainage of water, a unit support for supporting the external unit at a distance above the upper side of the base, a securing device for securing the holding system to the sloping roof, said securing device being configured to position the base and the wall substantially under the upper roof surface and to position the upper side of the base substantially horizontal or under a small angle in relation to the horizontal to in use guide water out of the water outlet, wherein the base or the wall comprises a holder opening to provide a passage for the interconnector and a water shield is provided at the holder opening to in use prevent the passage of water through the holder opening.