Setting the fan control (if you have one) to ON may help, since constant circulation tends to even out temperatures. Combined heating/cooling with ducts and registers is usually a compromise...with heat, in the floor with the natural lighter, hot air rising works well, but it is lousy for a/c, since that cool air pools near your feet. In an ideal world, you have both floor and high wall or ceiling registers, and depending on the season, you shut one or the other off. Dumping cool air from up high works much better than trying to force it up from the floor or lower wall. Similar thing with the return - in the winter, you want to collect the cold air near the floor and return it to be heated, but sucking the cold air from the floor and replacing it with colder air at the floor does little to make the vertical space a constant temperature, so a high return works better to suck the hot air out at the top. I have a relatively open floorplan, and have a return at the top of my staircase to the second floor (which actually has a skylight well going up to the roof at the actual skylight)...I suck the hot air from there, and tend to open the ceiling vents upstairs, and partially close off the vents downstairs, which forces more cold upstairs, which falls down. With probably R-60 in the attic now, to balance things, I can have the vents nearly even, upstairs and down and maintain 1-2 degrees difference between the floors. If you want to use a window type a/c for an upstairs problem area, you may want to look into a sleeve, and put it through the wall instead of through the window. This would also allow you to locate it higher up on the wall.