Inside heat control stuck on the warm setting

On my 1998 Mercury Mountaineer the temperature control on the dash, [the middle control], Temperature control is not functioning regardless of how I turn from Cooler to Warmer. Appears that something is stuck and ONLY warm air comes out of the vents, floor ducts, Etc. Dealer believes that possibly the door to the air mixing is broke/stuck. Has anyone had any simular experiences? Thanks

Yes, there is a vacuum acuator that controls the door. It may be stuck. Try manually operating the door and see if that frees it up.

I have ..or had that problem also. Doors locks were crapping out also. Traded in the 98 for an 02 ....gotta have that AWD where I live.