Mercury Sable Interior Climate

Hello, all. My 1990 Mercury Sable has developed a problem(s) with
dash/floor air and heat routing. Currently selecting the "vent" position
only results in warm (rather cold like it used to) air being sent out the
dash air ducts. Selecting "floor/panel" provides warm air out the dash
air ducts but air flow on the floor is barely noticebable even with the
"floor" only selection. The inside temperature selector appears to have
no effect - air is always warm (after engine warms up).

My hunch is that a vacuum-operated servo(s) that controls an air diverter
door(s) is non-functional but I would welcome any comment. Thanks for
your time. Sincerely,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337