That's supposed to say, "I'm HOPING some fellow old-home owners . . . "

I hate typos.

Upstairs rooms are usually hotter than downstairs rooms, because heat rises and the better the insulation in the attic, the more you'll notice that. It's not a bad thing.

If you have retrofitted air conditioning, and the register runs are old, you'll also find that the farther away from the unit, the warmer the room in summer. My mother's bedroom (upstairs) was also warmer in winter and especially summer than the rest of the house. Does she have a cold air return to facilitate convection? Is is blocked?

Yes, S.E. rooms in this latitude would also tend to be warmer from solar gain.

And lastly, go into your basement and look at the furnace runs. On each run, you may find a little 'key' on the outside of the run. It is an internal baffle to adjust air flow into each room, much like the register adjustments in the room. I never found these in old houses until a few years ago, and felt so silly I hadn't noticed them. We turned the key to register runs to my mother's bedroom to decrease the airflow in the run in wintertime and opened the other runs downstairs up. Some previous owner had adjusted them to their liking.

No cold air return in her room. I believe we only have one upstairs period, and that's in the hallway.

We have messed with the dampers as much as we can. It seems to make no difference. And again, this issue is especially frustrating on days like today (64 degrees) when it should be fine to open the windows and enjoy, but instead, we're running the AC to keep things comfortable in her room. The rest of the house is fine!

This is just a suggestion that falls under the slightly zany, but just may work category. I did it and it worked with our bathroom at the far end of the house/run. I changed the duct from putting out heat/air to an air return. The room now has no direct heat/air, but as all the air now circulates through there, the room does not feel any hotter or colder that the others. Ironically it also help to recycle moisture back into the house, good for us as we live in a dryer climate. :)

In our case it was just a matter of unscrewing the ductwork in the basement from the heater, putting a cap on the cut off "stub". I then used some flex ductwork to run in to the main air return (just before it goes into the heater).

Can you plant some trees on that side of the house? That should help with solar heat gain. Mature trees are pricey, but so is running the AC when it's 64 outside.

dainaadele.........that's an inspired idea.

In general, heat is lost through the windows and ceiling in winter and heat is gained through the windows and walls in summer.

For the window, they make reflective thermal linings for curtains. Regular shades/curtains reduce some of the heat, but the sun is coming through the window still and hitting the shades. Some energy is reflected and some is absorbed. If you can reflect more of the energy back out the window, you will get less heat gain. Also, if you love your current shades/curtains, they make reflective window films.

Walls are harder to fix. You can insulate them better or put up some sort of barrier. Trees are great in summer. Awnings work too.

I also have 1 upstairs room that is hotter than the rest even though it has an air return; it doesn't matter if it's winter or summer. Personally, I think it's because it's the room nearest the stairwell where the heat really builds up. We have fans in each room that run year round & a Hunter Original in the hall/stairwell that we run on high when the temperature rises. Leaving the door open to the hall coupled with the high speed of the Hunter, air circulation is greatly improved.