Abstract: An improved sealing cap in particular for a collector tube in an air-conditioning unit for vehicles suitable for being axially inserted in a cylindrical portion (11) at an end of said collector tube comprises at least two moulded elements able to be coupled (12, 13, 22), a first (12) element being equipped with a portion (16) with the same diameter as the collector and at least one portion with a smaller diameter (17, 21) suitable for stably receiving a second element (13, 22) to define at least one seat (15, 150) for a sealing ring (14), which is realised with the coupling of the at least two elements. The portion with a smaller diameter (17, 21) defines a base of the seat (15, 150), a side surface (19, 28) of the second element (13, 22) and a side surface (20, 29) of the portion with the same diameter as the collector (16) respectively defining sides of said seat (15, 150).