My 99 Mountaineer is equipped with the Electronic Auto Temperature Control. Just recently when the AC is on, the fan only blows at high speed, and when the temp gets to the point where the fan would usually automatically adjust to a lower speed, it doesn't. For a while it was intermittent, some days it would work and some it wouldn't. Now it is either full blast fan or no fan at all.

Has anyone experienced this and/or have any recommendations on what to check? In the old days I replaced many a Ford blower switches (toggles), but this being electronic I don't even know where to look. I found the fuse location, but everything else the fuse controls is working OK.

Any help would be appreciated.