Your blend door probably is not moving. The motor for the door is on the bottom of the heater box above the trans tunnel. It is attached by three screws to the heater box. Start by taking the motor off the blend door shaft and see if it moves freely. If it does, then I suspect the axle for the blend door is broken and that means the heater box must come out to fix it.
WANTED--MJ Comanche to restore. Must be solid, (relatively) rust free chassis. Send me a PM if you have a line on one that is for sale.