I've moved into a 15 year old house which is about 3200sf across 3 floors. The lowest level is about half of the total area, and is cooled by a newer 2.5 ton unit. The main kitchen/dining/living level and the upper master bedroom make up the other 1600 square feet. This is a lake house, with a view to the east. From the main living space, there's probably 300sf worth of window, and from the master bedroom, there's another 150sf. This main level and upper level are cooled by an original 4ton unit.

Since it's gotten in the 90s and low 100s here in central indiana (!!), the main and upper levels have gotten hotter over the course of the day, topping out around 82 in early evening. This is true even with the solar shades on all the windows drawn all day. The unit runs between 18 and 20 hours each day with the thermostat set at 74.

I had a service company check the unit, via our home warranty company, and they cleaned the condenser coils, and replaced the outdoor fan motor, contacter, and capacitor. They said the coolant pressure was perfect. These fixes didn't seem to help.

Getting service this way is pretty grueling, since I have to go with whatever company the warranty company chooses. If I choose my own service company, they won't pay for repairs. So, I'm trying to understand what might be causing this before I decide whether to call for another repair, or whether this is a design problem.

I've opened up the evaporator coil and measured a very big drop between the hot and cold side of the coil. it's about 82-85 degrees on the hot side, and between 45 and 50 on the cold side. But the air coming from the vents is closer to 70. Would this indicate an airflow issue, or possibly a leak in the ductboard in the attic?