SAC should have been cut back to the ground once each early spring. It is a "type 3" clematis that gets pruned to the ground.
In spring (about the time the forsythia's start to bloom) prune it down all the way to the ground or at most to 6 inches high. Don't worry it'll grow back fast! :)
I am also in Ohio, north east Ohio near Cleveland. :)

If it has already developed a very woody base, cutting back to 6" may be a bit severe. You can cut back to the third set of buds from the base or somewhere around 18-24" above the ground and that will still accomplish the same thing. btw, this should be the practice with any type 3 clematis that has some age and substantial size to the trunk or lower stems.