Okay, I have searched several forums and have not found any discussion directly related to the problem with the heater - A/C vents in my truck.

My system basically works with the exception of the dash vents. I can switch from floor to defrost and floor-defrost combo. But when switched to dash vent or dash vent-floor combo it will not blow any air out of the dash vents and defaults to blowing air out of both the defrost and floor vents. I can up reach under the dash and manually pull the dash vent control and get air out of the dash vents. The vacuum line going to the vacuum actuator that controls the dash vents has vacuum, although I am not sure has much it is supposed to have. Is it common for the vacuum actuator itself to go bad? I hate to just start throwing parts at it not know what is wrong and hoping one them fixes the problem. Is there a way to test the vacuum actuators?

 

I'd bet money your actuator is bad, I replaced mine, cost about $30, pretty easy to swap out, just a dlight pain to reach due to the location. I had to get mine from the dealer.