no defrost??? what the heck??

[rs74]

If your blend door is moving when changing modes then I would think it should be redirecting air where it is supposed to. Let me ask you this. Did you unhook the piece of all thread and with the truck running and manually push the door and hold it in both directions to see if it went to defrost 100%. Still sounds like the blend door is not either opening or closing 100% so your direction of air changes.