There are several reasons hat could contribute to it. One of the biggest reasons is dark colored shingles on the roof, Dark colors tend to hold heat and transfer it to the interior. Lack of ventilation in the attic space. Good ventilation gets rid of heat more quickly. If it is sunny outside the walls act as a heat sinc and will hold heat thus allowing it to transfer to the interior. Ways to min this is insulation being properly installed. Also you can plant trees on the south side of the house. Trees will shade the house and help keep it cool.
mine is always 80 when i turn it off, doesnt stay off very long :/
The home still has residual heat in the walls and attic.
try opening the window ;)
Are you upstairs or in the direct sunlight? That will do it.
Blame it on global warming