1 year-old unit NOT cooling...

This one is a doozy. I had a technician come out and increase my subcooling from 5.2 to 9.6. He mentioned that the second tech dispatched to my home completely missed this issue, though I don't know why. The unit was installed in July 2025.

The house feels warm on hot days. The tech was out last Friday and said the unit is working properly. I saw the pressures on his guage and the subcooling was overing over a 9.5/9.6, but the ambient temperature was only in the high 70s to low 80s. He is returning this Wednesday when the ambient temperature hits 90°F to verify that the system is struggling. Hopefully, it doesn't make a liar out of me! The unit cools okay on less hotter days!

My home is 1,478 sq. ft. and the unit is a 2.5-ton system running on R-454B refrigerant. In April, I insulated my attic to R-49, which the tech visually verified and noted. The windows are also fairly new. Paying a pretty penny for a brand-new unit that fails to cool on hot days is unacceptable. What do you think is happening?