defrost dam stuck

hello my name is justin from lethbridge alberta, i have a 1982 chevy silverado. a few years ago we started a lot of engine work and unfortunately got the wrong guys to do it in the first place. they took the original 350 and ripped it all out. we also said that we would not need the a/c and they ripped most of that stuff out except for the actual unit that the freeon is in. long story short the first engine seized about aweek after it was put in and we got screwed. anyway about a year ago we got in touch with a local rebiuld shop and they hooked us up with a nice rebiult 350. nothing too special becuase it is an everyday driver. i notice most of the requests are for newer vehicles so i hope you can help me. the new engine only has about 4500 miles on it. the aluminum valve covers leak a little bit of oil but other than that it runs great. lately winter came up really quick and i noticed that the lever on my heat control that selects air, heat yada yada, then defrost is all the way to the right. does not do anything. when you move it to off which is all the way to the left it will shut it off but other than that it does not change anything. the lever below that to control the hot or cold dam works fine. it is just on a cable and works fine. but also the fan control on the left will not select a speed for the fan. the first three notches do not do anything then when you push it all the way up the fan starts blasting air. all i need to do for the winter is get that defrost dam to open somehow. then i can rip it all apart in the spring and do it all right. so is the heater control the problem or could it have something to do with those monkey ripping all the a/c stuff out? so if you could help me i would very much apreciate it. it seems like you guys have a very large wealth of knowledge according to all the other questions i have read. i hope you can help me out. thank you for your time and hope to hear from you soon.
p.s. sorry for beeing a little long winded