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.
1992 XJ 2" lift -- RIP
2000 XJ 3" lift -- Australian Ford Big Brakes up front, rock rails, ZJ rear discs (with WORKING parking brake), C4x4 rear bumper/tire carrier, Hella H4 headlights, IPF driving lights, OEM skid plates, OME springs/shocks, JKS LCA's, JKS Sway Bar links.