1 Answer

The selector switch should be controlled  by manual throw cable, vacuum throw that actuates the lever or possibly an electric switch might control the selection. I first would look under the dash directly under the throw lever and see if you have access to switch. If not one might have to remove a trim panel or even an a/c or heat duct to gain access. This will determine what selective device your vehicle has. If unsure about self repair? Call your local library and see if they have a specific repair manual for your truck year and model.(Chilton) If so, go and look at trouble shooting tree diagram for your problem No heat,heat but cannot select defrost etc.If you feel this something you can do? study the area it directs you to fix problem in repair manual until confident then go for it. You can also purchase repair manual from your local auto parts store for under $30 to $40 dollar range approx. Keep in mind  dealerships vary on labor cost anywhere from $75.00 to $125.00 per hr approx. depending location Personally, I have seen the time where I found a vacuum hose got pulled off and put it on the only empty available nipple. Bingo it worked. If it is controlled by electric switch check your fuses. Good? check to see if electrical connectors not come lose or off. Suspect switch? check repair book on how to check switch to see if failed? Good Luck...This selector switch controld the divertor door to select heat,defrost and so on.If selector moves freely but it stays on heat its probably disconnected. If the lever does not move its probably cable assited and in a bind or guide of cable is lose causing failure.