A casing houses a heat exchanger in a vehicle HVAC system. The heat exchanger includes air inlet and air outlet faces, rear end and front end faces, and first and second side faces. The side faces are each capped with a radiator tank comprising a front end. Each radiator tank defines an orifice for connection to a heat transfer fluid supply circuit. The casing includes a front end wall defining an opening opposite the front end face of the heat-exchanger. The casing also includes a cover defining at least two passages adapted to suit the orifices of the radiator tanks and fixedly attached to the front end wall. The cover also includes seals for limiting the outlet of air via the opening and/or the passages.