Nothing appears to be functioning on my climate control. No fan or other control. Constant heat emitted from defrost however, without fan blowing it out. Any help greatly appreciated!!!

Defrost heat only is the fail mode. MB feels that a clear fog free window is important at all times!
In any respect you could be looking at many different issues and some of which are hard to track down.
The simplest assumtion is your pushbutton unit, however it could also be your monovalve, temperature interlock sensor, fan regulator or temp regulator. You may also have a diaphram, vacuum issue. You have to do some detective work.
BTW how many miles, any recent ACC parts replaced.
On my 84 I chased this issue from stern to stem and found I had a short AND the wrong temp interlock sensor (temp range).
Good luck