Defrost Question

[noclrnce]

I have an 83 K10 non ac truck. When I turn the defrost on it doesn't seem like it blows out like it should. It also seems that when I change the speed it doesn't change. Even if I turn it off it still runs. Can anyone give me some ideas on what to check?

[slotard]

I know I read somewhere that even off blows because they wanted to make sure the cabin was ventilated adequately. Mine does the same thing though, don't know why.