I just finished fixing the blend door on my '96 Explorer. The easiest fix is the actuator only (if it isn't working). You can check it by pulling just the actuator and cycling the hot/cold control with the engine running (or at least with power to the HVAC). If the actuator turns, the problem is the blend door itself. They have a tendency to break near the top of the hinge shaft like mine did. I have a few shots of what I did.

For larger images, go to the photobucket album at http://photobucket.com/blend_door.

So, first, remove the actuator by taking out the two screws in front and popping off the white actuator enclosure. If the back is bolted, you will have to break the back bolt out of the plastic housing with a large flat bladed screwdriver, unless you have really tiny hands and a very slim ratchet wrench.

The fix I used involved cutting the bottom of the plenum with a dremel tool (using spiral cutter at low speed), extracting the door and then repairing it. The opening should be roughly a half rectangle. Cut close to, but not into the round projection seen at left. That is where the bottom of the door hinges. The shot below shows where I didn't cut close enough and the door would not fit through the opening.




The door was broken near the top, and I was able to retrieve the broken piece.




I cut a piece of 1/2" copper tubing and then slit it so I could use it as a splint over the break. I super-glued the broken pieces together to make it easier to assemble.




I widened the slit with a screwdriver so it would just fit over the spine. The ID is almost a perfect fit.



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Once assembled, I drilled a hole .002 smaller than the wire size of a couple of wire nails, then tapped them in and cut and filed the points.



Getting the door back in was difficult, but shaving off the top and bottom of the "shaft" gave just enough clearance to muscle the door back together. I shaved the top at an angle to help get the door back in as you can see, below.



Below is the door reinstalled as seen through the opening in the bottom of the plenum.
Check out the heatertreater.net for a replacement door that is much easier to reinstall, but costs $119. He also has a GREAT video explaining the repair procedure and exactly where to cut.




The last step is to duct tape the piece you cut back onto the plenum. I used metal foil tape that is much tackier than regular duct tape and lasts longer. Happy repairs! By the way, this probably saved me $1000 and the cost was zero cash and only a couple of hours of effort.