I have a 2005 Lincoln LS...and my heater blows very hot even when I adjust my dual temperatures. I have to shut the vents cause the air coming out is so hot. I did try and turn my AC on to see what would happen and I could only feel cooler air out of half of my vents. The air wasn't very cold but I could tell a difference in the temperatures.

Any ideas?

98% odds that you have a failed DCCV.