99 Sierra has no heat

99 Sierra pickup has no heat.
I flushed the heater coil and have hot water both sides.
Fuse is ok.
Blower and control for vents, defrost works ok.
Turning the cold to hot control, temp stays the same, although it sounds like something is moving, but not certain what the noise may be.
Just for info, the instrument cluster needs to be replaced, but I can't see where that could be related.

you should take off the air temp door motor and see if you can change the temperature by moving the door manually.the motor could be bad, the door could be stuck or the door could be broken.