System housing, in particular for a heating, ventilating and/or air-conditioning system of a vehicle, comprising at least three housing parts, which serve for accommodating air-conditioning-system components and/or for forming air-channeling paths, one of the housing parts comprising a first abutment surface and a second abutment surface, up to which the other two housing parts can be advanced in each case parallel to a normal vector of the abutment surface which is advanced up in each case.