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 -- stock (RIP)
2000 XJ -- lots of basic mods. Sold to fellow forum member. I miss it.
2014 JK -- the project is just starting!
For Sale to Good Home---2000 XJ Factory Service Manual (Printed Version) PM for details.