I have a 2000 ML and I think there may have been a change such that the later one's are more complicated.

I did this a month ago. I could not go through the instuerment cluster.

First, I would pry out the center duct. Then you should be able to see the motor. Turn on conditioning and move dial from hot to cold to see if bell crank is moving. If not working it jerks and clicks.

Having removed the dash I think it might be possable to go in through the center vent if one really knew what there where doing. Would need to know how to un plug the motor, small hands, and a flex screw driver. I think you have two screews. Leave the bell crank in place.

Do some research on dash dissesimbly. The radio needs to come out. This takes a special key. I found a local stero company to unlock it for free.

Should use plastic pry tools. Open side door's and pull side window defronter vents, then side vents, then center vents. They just pry out. Remove spedo cluster (look up how), pry out center ac control consoule pannel. Keep track of all fasterners. Take out glove box. Remove lower dash. Need torx for screws at sides of dash. Remove dash top defroster and screws under. Start hunting of all the little screws that hold the dash on. The manifold that supplies the vents stays mounted to the dash so do not try to un screw it like I did.

I know this is not a good description of how to. It will give you an idea how much work is needed for this bugger.

Took me the better part of a day. Was very rewarding as the dealer quoted somthing like $1200.