you need to install everything associated with it. all the lines, all the parts (including a new heater box core), and the in-dash stuff to make it all work. Assuming you get the right stuff, it all bolts in. It's just a very elaborate bolt-in affair. A matching parts XJ with functional AC would be the ticket.
Oh, and convert the dang thing to the new refrigerant while you're at it. :thumbsup: