I've got a 1990 Z71. I'm getting cold air from the blend door. I took the fan assembly out so I could see what's going on. When I turn the key on the blend door goes all the way down cutting off recirculation and letting in nothing but outside air. When I cut the key off it goes all the way up allowing both recirculation and fresh air in. Nothing I push on the heater control makes the blend door move. How is this thing suppose to operate? It's freezing me to death. I replaced the actuator, still the same thing. Do you have to calibrate it? I've read some of the newer trucks have to calibrate. If so why did this happen in the first place to the old actuator? Can someone tell me what is suppose to control the blend door?? I hear the other door moving when I move the temp from hot to cold so I know it's working.