Arrangement comprising a service port (30, 40) being attachable to a refrigerant line of an air conditioning system, said service port (30, 40) having a circumferential direction and a groove (32, 42) in said circumferential direction formed therein to which a device can be attached, an extension (34, 44) beyond the groove (32, 42), a collar (38, 48) in said circumferential direction between the groove (32, 42) and the extension (34, 44) and an end (36, 46), a device for preventing refrigerant leaks in air conditioning system service ports (30, 40), the device comprising: a coupler to be coupled to the air conditioning system service port (30, 40), wherein said coupler is a quick coupler having a detent for engaging in the groove (32, 42) formed in the service port (30, 40); a main body (6, 6') having a longitudinal direction, an open end and being disposed adjacent said coupler in said longitudinal direction, wherein the end (36, 46) of the port (30, 40) can be inserted into said open end; a stem movable inside said main body (6, 6') in said longitudinal direction; a sealing element adjacent said stem; a head fastened to said main body (6, 6'), said head having an internal thread; and a handle having a shaft with an external thread to be screwed into said internal thread of said head, said shaft having a free end remote from said handle for contacting said stem and pushing said sealing element adjacent said stem against said end (36, 46) of the service port (30, 10) upon turning said handle. a service port (30, 40) being attachable to a refrigerant line of an air conditioning system, said service port (30, 40) having a circumferential direction and a groove (32, 42) in said circumferential direction formed therein to which a device can be attached, an extension (34, 44) beyond the groove (32, 42), a collar (38, 48) in said circumferential direction between the groove (32, 42) and the extension (34, 44) and an end (36, 46), a device for preventing refrigerant leaks in air conditioning system service ports (30, 40), the device comprising: a coupler to be coupled to the air conditioning system service port (30, 40), wherein said coupler is a quick coupler having a detent for engaging in the groove (32, 42) formed in the service port (30, 40); a main body (6, 6') having a longitudinal direction, an open end and being disposed adjacent said coupler in said longitudinal direction, wherein the end (36, 46) of the port (30, 40) can be inserted into said open end; a stem movable inside said main body (6, 6') in said longitudinal direction; a sealing element adjacent said stem; a head fastened to said main body (6, 6'), said head having an internal thread; and a handle having a shaft with an external thread to be screwed into said internal thread of said head, said shaft having a free end remote from said handle for contacting said stem and pushing said sealing element adjacent said stem against said end (36, 46) of the service port (30, 10) upon turning said handle. a coupler to be coupled to the air conditioning system service port (30, 40), wherein said coupler is a quick coupler having a detent for engaging in the groove (32, 42) formed in the service port (30, 40); a main body (6, 6') having a longitudinal direction, an open end and being disposed adjacent said coupler in said longitudinal direction, wherein the end (36, 46) of the port (30, 40) can be inserted into said open end; a stem movable inside said main body (6, 6') in said longitudinal direction; a sealing element adjacent said stem; a head fastened to said main body (6, 6'), said head having an internal thread; and a handle having a shaft with an external thread to be screwed into said internal thread of said head, said shaft having a free end remote from said handle for contacting said stem and pushing said sealing element adjacent said stem against said end (36, 46) of the service port (30, 10) upon turning said handle.