Is this my acc servo or monovalve or what..???

[Astroman]

Ok, here's the situation. Yes, I've gone blind searching threads, but no one seems to have had exactly the problem I have. 1981 300SD. I have noticed that occasionally my left-center vent will start blowing a little warm air (yes, just that one) and if I cycle the modes on the accu it goes back to cool ec air. Last night I was driving home and the whole system went full hot, enough in fact to noticeably cool the engine temperature. One would think this would indicate monovalve, and maybe that's part of the problem, but I could actually hear the vacuum servos under the dash changing when this occurred. After cycling through the various modes a few times and, listening to all the vacuum servos flapping around, everything returned to normal.... I'm on my way out to check the tube for the temperature probe, but I'm a little skeptical. Any ideas on this one?