Need an old timer lennox expert.

I kinda take over a converted old hotel renovated in the late 70s with two of these beast on the roof, 24 zones each. system is from 1979, still in full operation. the building now is an office complex that has been diced up and cut up through out the years. found a board room that's fed by two different zone, I endup fixing all the t-stat to the same temp to combat those zones cancelling each outher out. I found some info on it, but still don't understand it. another company used to take care this building, they're not getting called in for whatever reason, and the tech that works on this bldg is now at another company. I do have a way of contacting him if I need to, but I don't know him that well, only met several times so far.

- would someone explain to me in plain english on how this system work?
- what's turning the fan and heat/cooling on and off? what's controlling the temp/demand for cooling/heat?
- how does this cold deck/hot deck shebang works?
- is the zone control powered by the unit or is it on different power source?
- I'm also looking for service bulletins/manuals on how to tackle this if any body has some pdf.

thx for your help.