My home was built in 1996. It is a 2 story 2000 square foot home. I am the second owner of the home and have lived here for 6 years. For the entire time, when summer time comes, the house has a very hard time cooling the upstairs (never a problem heating in the winter).
I have a Carrier AC that had its coils replaced 3 years ago.
I thought the source of the problem was probably a few things.... 1) poor airflow upstairs, 2) heat from windows, 3) attic heat seaping down into the rooms.
Over the past year, I have done the following:
Installed a zoned system. I did this myself, and the airflow upstairs, when the downstairs zone is not calling for cool, is much much better than before. This seemed to make the heating equalized for the first time in the summer. It did seem to improve cooling upstairs in the moderately hot times (85-90), but on 90+ degree days, the upstairs would start to warm up around 3 PM, and peak around 9-10PM (the upstairs always get hot AFTER the peak of the day).
I then installed GILA window tinting on all upstairs windows, and installed blinds on any windows that did not have them. A little more difference was noted, but not too much.
I installed an attic fan [1600 CFM] (I already have soffits).
I then had my attic blow to an R-49 rating.
All this added together has made an improvement, but my home still gets warm upstairs. I installed a remote temperature relay so I could see how hot the attic is getting. This was done unfortunately after the attic fan was installed, so I don't know what the temperature was before the fan. On the hottest days (around 98 degrees), the attic will see a temperature around 120 degrees. This is kinda what happens:
around 9AM after a previously hot day (90+ degrees):
Downstairs unit set to 73. Its not calling for air.
Upstairs unit set to 73. Its not calling for air. it spent the night getting the temperature back to normal.
The day is going to have a high in the mid nineties.
from 9AM-Noon, the upstairs controller only calls for air every now and then. temperature remains around 73. By this time, the attic has already peaked 90 degrees.
Around 1-3PM, the upstairs begins to slightly warm. The controller calls for cool, and starts to get behind the curve (the unit is calling to maintain 73 degrees, but by 3 PM, the upstairs is up to 74.5).
the downstairs controller starts to call for air every now and then, but maintains 73.
From 3-5PM, the upstairs starts to go around 75 degrees. The attic temp is peaking around 110-120. The downstairs controller starts to cycle more often.
After 5PM. Both controllers call for cool.
After 7PM. The attic has cooled down around 15 degrees. Both controllers call for air, and both units can't maintain. The upstairs is now around 77-78 degrees, and the downstairs is 75.
after 9PM both units start to catch-up, and the temps start to drop, but it is not uncommon to see the temp upstairs over 75 until around 11PM, sometimes later if the day was really really hot.
I have typed all this, so its possible this can give you a better idea of the source of heat and how to deal with it. Buying a new unit is not an option at the moment. Thank you very much for reading.