Home Wiring Saga (or the Undiscovered Country)

Today I made the decision to finally install a digital thermostat for my home cooler.  Prior to its installation, the former method had been a rather rudimentary five-way switch, no adaptive temperature control, a number of prayers, and an astronomical electric bill. 
Being a responsible homeowner and an advocate for safety when recklessness wouldn’t be any fun, I sought to turn off the power to the hallway I was working in.  So I turned the hall light on, retreated to the circuit box, and began flipping switches.  Some things I noticed:

1. No switch appears to turn off the lights in the Spare Oom.  The source of this room’s magical energy still eludes me.
2. Even after getting the hall light to turn off, the selfsame switch did NOT turn the AC off, even though the two units are not even one square meter apart.
3. Turns out, the AC is wired to the same breaker as the office, which are separated from each other by a kitchen, a dining room, and a living room.

Being the steward of self discovery that I am, however, I subsequently dismantled the AC control unit (after solving the power access mystery).  At first, everything was self explanatory.  The new thermostat unit came with detailed instructions.  But then came the matter of “the ground.”
For the uninitiated, in the world of household voltage, “the ground” basically diverts an electrical short to the conduit box and through the house, as opposed to say, through your hand (read: useful).  Many houses as old as mine have no ground wire running directly from the AC unit on the roof (which is now the standard).  No big deal.  HOWEVER, upon inspection of the previously-mentioned rudimentary switch, I discovered that the former installer had simply clipped the errant ground wire for the control unit, LEFT IT BARE, and then closed it all up soundly within my plaster walls.
So, in a way, I’m a hero.