Temperature Control System: Innaccurate

[Esquire]

I have a '91 300E.

When I have set the temperature at a certain level (e.g., 75 degrees) - the selected temperature being in the center of the dial -- I find that the air is too cool to match the selected temperature. It does become hot when I crank it up -- just not the correct level.

Is there anything adjustable there -- or is the temperature receiving unit (by the sunroof switch) having a problem (incorrect voltage)?

I addition - is there an airfilter for air coming into the car that can be changed/checked -- When I push the "recirculate" switch -- sometime I can still smell that nasty diesel smoke.

THANKS!