2005 Chevy Monte Carlo heat vent problem

I had the same problem with my 05. At first I thought it would of been my left side temp actuator so I went ahead and removed it. I tested it out with 4D batteries and it still moved back and forward. Then I tried moving the blend door with my hand in place of the actuator. I felt heat come out on the floor. So I assume that the door was jammed on something or just stuck. So most likely it's your blend door which is a very easy fix. You will have to remove the knee bolsters under your steering column to get to the actuator. It'll be placed toward the center of the dash. You'll be able to see it if you lay down on the floor on the drivers side.