Climate Controls stuck in bi-level position

Curious if anyone here had the same problem. The vehicle is the 99' S-10. All air blows out the mid-level dash vents only. I was told by my backyard mechanic the problem is not a vaccuum line detached - instead there's two air divert-motors under the dash that requires tearing the entire dash apart to figure out which one is the culprit. Hoping to find a differing opinion here.

Thanks in advance
Joe