Who/how was it determined that "I have 225 amp main line power to my home"? That is not the usual terminology used to describe the service size. Assuming that you really do have a 225 amp service (Durham does make such direct-reading meter sockets), it should be adequate for adding the AC. You need a GOOD electrician on site to answer your questions. Here is a link that might be useful: Durham

Jake, what is the best way to clean a molded-case circuit breaker well, that's easy-you use dry chlorine bleach, of course!

"So, in the current setup or as I have diagramed above still maintaining a single circuit, is this system inadequately grounded?" As a single circuit, it is presumably grounded just fine, as long as there is a proper grounding electrode system back at the main house panel. "I had assumed the circuit being fed consisted of a live, neutral and ground (the twisted bare). " As it is set up at the current time, that is correct, but it wasn't originally wired that way when the actual wire was installed. They didn't DO ground wires back then, and a "bare wire" does not infer that it is a ground wire, just not "ungrounded" (HOT). That is a cable with a concentric neutral. I doubt that either of the insulated wires are "identified" as a neutral (white insulation). "200.2 (A) Insulation. The grounded conductor (neutral), WHERE INSULATED, shall have insulation that is (1) suitable, other than color, for any ungrounded conductor of the same circuit on....." "200 .6 Means of Identifying Grounded Conductors. (A) Sizes 6 AWG or Smaller. An INSULATED grounded conductor (neutral) of 6 AWG or smaller shall be identified by a continuous white or gray outer finish or by three continuous white stripes on other than green insulation along its entire length. Wires that have their outer covering finished to show a white or gray color but have colored tracer...." "Regarding the disconnect... " This depends on the final decision of how you wire it. As it is wired right now, you would only need a standard toggle switch (just like the ones that turn on the lights). If you make it 2 circuits, you may only need 2 standard toggle switches, (just like I cut and pasted them out of your original drawing). You really only need something that looks more industrial if you need to install over current devices. Do you know what the actual wire gauge of the cable going from the house to the garage is? Back then, a common thing to do was to put a dryer receptacle in the garage. (Funny enough, I just noticed that there is a documentary on the outlawing of clothes lines in many parts of the country when the dryer became popular.) In other words, that may have originally been a 30 amp wire and a gas line to make provisions for either type of clothes dryer.

Sorry I wasn’t clear. There is no thermostat at all in this room. The main part of the house (built 1978) is on a heat pump w/auxiliary electric heat and has a thermostat as you’d expect. This room is an addition that was built in 1987. All we have are baseboard heaters with an individual ‘dial’ - not a real thermostat. There is no wall thermostat. I want to hook all three of the baseboard heaters up to a single thermostat. Part of the issue is that I don’t even know where the wires run through the wall.