From what you have said so far, I assume this to be a package unit (one single piece of equipment, containing the entire system except the thermostat) is this correct?
Yes, that's right.
You mentioned climbing up on the roof to find a model or serial number. Is this package unit mounted on the roof? If yes, how does the air enter the house?
Yes, it is a single unit on the roof. The return air goes up from the hallway and the ducts are descending down from the unit.
It's 30 years old? Pretty dadblamed old for a compressor bearing anything.
I've got the home warranty that is taking care of it. The air handler motor died last winter and was replaced, along with the condenser fan motor (the blades were unbalanced and they couldn't take them off, so they've just replaced the whole module). My guess is that it's been patched over a thousand times.
Have you begun any of the interfacing to automate your damper system?
Yes and no. I've solved the problem of controlling the dampers (though this subsystem is inactive yet), but didn't implement the A/C controller itself yet.
I wondered because I noticed some rooms track different than others.
Well, that's exactly the reason I started to work on the controller in the first place. See, the thermostat is installed in the room that is represented by the red line, and the sensor doesn't care about the temperature in the other rooms, and if it so happens that those rooms heat (or cool) faster (or slower), the difference appears. The lower the ambient temperature, the more is the offset between the red line and the others. The offset can reach 10F.
You use a setback thermostat I take it? Or do you just turn the heat down manually every morning when you get dressed? Or is that permanent drop a symptom of the failure? If you do have a setback t-stat, what kind?
Yes, it is a setback thermostat. Honeywell Chronotherm III. By specs, pretty smart, in reality, not quite so.
I am curious about whether you have supplemental heat or not, but that is not something I can expect you to tell me.
Since I don't know the exact answer, I'll try to put it this way: the roof mounted unit is the only source of heat, not counting the house's internal heat sources (fridge, TV, etc.)
So, that's my questions and thoughts. Once I have that equipment type, I'll be able to fill in some gaps. If you were without heat, I would be telling you to call a pro, but at this point, you are only uncomfortable for an hour or so each night?
I'm not even uncomfortable, I don't even notice it until I look at the graphs. However, since I've invested quite a bit of time into the understanding of how this stuff works, and it doesn't work as expected, my technical nature rebels
Are those two plots from sucessive nights?
Yes, that's right. On all the previous nights it was just cycling normally.