Had new amana split unit installed in February it heated house OK, but since its got warm , the unit will not cool house to the 72 set point. Its 80 outside now and its 78 in my house and the unit is constant running. The tech has came out 3 times and the last time he came he said he couldn't figure out what's wrong that he's checked everything. My power bill is going to be out the roof,what can I do

What tonnage is the unit, what is the square footage of the house, how well insulated is the house ,how much insulation in attic, are ducts insulated and properly sized all this has to be known before any suggestions are made.