I requested and received several Evo TSB's from NHTSA including one entitled “Heater Temperature Dial Hard to Turn”. I ordered this particular TSB (TSB-05-55-003 issued December 2005) amongst others because my car is an affected vehicle and I plan to make this repair.

The TSB states that the cause is the blend door link and lever binding, or a dirty and/or damaged blend door gear track. By the way, these parts are on the outside of the heater box. The repair is to install a new improved heater blend door inside the heater box.

So, the cause is one thing and the repair is something else. It may help your understanding of this inconsistency by noting that the TSB this TSB supersedes called for replacement of outside linkage only. This would have been a much less costly warranty expense for Mitsu had it worked.

This TSB also calls for installing a filter on the heater box intake to prevent the ingestion of debris's.

The complete parts listing is as follows:
Heater blend door kit 7801A360
Heater blend link and lever kit 7801A110
Blower motor housing filter MN185231
Screw (2) MF453032

I suspect the only part needed is the door kit unless the control linkage has become damaged by the excessive force needed to move the blend door.

The filter would be a good idea for owners who park under trees. You might also regard this as a nice addition to your vehicle, most new cars now come with them. However, the filter requires periodic replacement.