I replaced my old air conditioner with a Trane 11/2 ton unit which is the same size I had, but on hot days the coolest I can get the house is 74 and on days when the outside temp. is 80 the unit runs constantly do you think the unit is to small?

How long has it been since the install? Call the installer,, could be its over-charged on freon,

Unit was instlalled in Aug. 09, Had the installer check it over last weekend said every thing charged OK right with spects. He adjusted blower speed but it still acts about the same maybe a little better.