So I think I have come into my first problem on my 08 Titan. Leaving work last night it was about 39 degrees out so I let my truck warm up like usual, once warmed up I started going to the gym and I turned the heat on, it blew nothing but cold air on like the ac was on. I checked everything it was on heat. I figured once I turn off the truck it will reset itself and work like normal. So after I am done at the gym it is about 31* out, after the truck warms up I try the heater again, same thing. I woke up this morning and it is still doing it. Any help or suggestions on how to fix this? Sorry about the long post.