Abstract: A heating and/or air conditioning installation for a motor vehicle includes a wall having a through hole. A temperature sensor has a heat sensitive element lying in a housing, which may for example be formed in an evaporator of the air conditioning installation. The sensor has protruding connecting wires surrounded by a sheath, and is attached through the hole in the wall by a fastening device. The fastening device comprises a tubular body portion adapted to be removably held fast in the hole, together with a sleeve portion joined to the inside of the body portion and having a passage through which the sheath passes. The sleeve portion has a narrow end which grips the sheath, and a wide end facing towards the heat sensitive element and affording some freedom of lateral movement to the connecting wires.