Hey all, OK, I pulled my dash, and replaced the vacuum lines going from the interior to the engine compartment. I also replaced the lines going from the heater/temperature control to the connector under the glove compartment. Now I finally have heat, BUT I needed to take a Zip-Tie and hold the Vacuum valve in the Heat position because I can't get it to work just off vaccum. I don't know where the issue is but I have two lines coming from the interior, one goes to the valve, and one gost to a "Tee" the other line going into the Tee comes from the Heater Housing, and the third line comes off the Vacuum tree on the side of my 4.9L. When i start the truck and disconnect the lines I can hear and feel vaccum. But it doesn't seem to change when i move the heater controls in the truck. I am wondering if the control piece itself is bad. All the doors function, I switch from Defrost to Heat and Floor no problem, Just couldn't get the heat.... now today for the first time I did get it after I had replaced lines and zip-tied the valve...I would like it to work as it should though and am trying to figute it out. Any advice

 

Check the blend door, may be clogged up or bad seal.