1983 300SD-Turbo, W126--air conditioning problems

[Mike-1983 300SD]

(1983 300SD-Turbo, W126) Initially, I was having some "vent" problems over the last couple months (in both heat and air conditioning mode) which I am fairly certain are the result of diaphram leaks (that I can fix). So far, these problems have just meant aggravations with cool air coming only from top vents blowing on windshield and fogging windshield, not to mention the conditioned air cooling the windshield and not me. The problem progessively got worse so that I could only get cold air when the temp dial was spun all the way around to MIN-(dial blue). Now, with the Climate Control Unit turned on (a selection button depressed) the fan will not come on, regardles of "High, Low, or Auto" speed setting. I do get a slight volume of warm air coming from the top vents, which I understand is the default setting to at least defrost the windows in event of system failure. Occassionly, the climate control system will come on (top vents only) and run in whatever mode heat/cool it was in ( cooling, only if set to "MIN"-blue). When it does come on, I can sometimes change mode (heat-to-cool or vice versa) and it may run for a few minutes, or it may just shut-off completely when I turn the temp dial from/to MIN.
My first thoughts are that it is a problem in the Climate Control Unit (pushbutton unit) since things seemed to go haywire when I strat turning the temp dial. After reading some of the other threads, I am wondering if instead it is a vaccum issue or low voltage issue. One other symptom, when the blower/fan does come on, it sounds like it is starting slow, struggling to get up to speed for the first 5-10 seconds before it runs "normally". Help !!! It is starting to get hot down here in North Carolina. Any ideas ? (oh yeah, "Go UNC-Tarheels" basketball)