Faulty rear module for rear heat on passenger rear. At the beginning, when I turn it up, it will wait for about half an hour before it comes out. Progressively, it starts making a clicking sound every 2 seconds or so for about 15 minutes. Now it stops completely. No more air on the back. Continuous replacement in order to have heat on the back of truck created a new problem with the front heat as well that I have to keep replacing from now and then..