We have a newly built house that the AC is taking longer than I would expect to drop the temp 2 degrees. I'm wondering how long we should expect it to run under the conditions I've specified below. Any help would be really appreciated.
1950 sq ft new construction house, single story + basement
R60 Ceiling insulation
R19 - 2x6 walls
house faces north with AC unit at the front of the house
there are large windows to the south of the house but no windows on the east and very few on the west
the AC unit is a 3 ton 13 seer Carrier 24ABB
The house temp was maintained at 78 deg from 4:00pm to 9:00pm. At approx 9:00 pm the thermostat kicked down to 76 deg. The outside temp was 75 deg with the sun fully set but it was more humid than inside (not horribly) but enough that to sleep comfortably we wanted to keep the air on.
The AC ran for 120 min straight never shutting off, to drop the temp to 76 deg.
We also run a dehumidifier in the basement that keeps the humidity down there at approx 55%.
This seemed excessive to me based on our past 15 year old house with a 15 year old AC unit. That would typically take 30 min maybe 45 min to kick the temp down 2 deg.
I called our HVAC contractor and he said he checked everything out and it's running fine. He said that because we don't have any blinds (haven't gotten any yet, we just moved a month ago) the radiant heat coming from the windows was causing it to run this long. This seemed like a bad excuse to me. I understand the concept of radiant heat and do not believe this would be enough of a cause for the AC unit to run this long with the temp being that low outside and no sun.
I'm just wondering what should be expected under these conditions. Thanks for any help you can give me. If you need any more info please let me know.