My new cooling unit from Reliance is not cooling the house even though it is a commercial system. I have set the temperature at 70, but its 81 inside the house. The company person from Reliance came today and checked the cooling at the vent which is 55. And he said that the filter is also fine. He gave OK report and left and I'm still sitting in room with temperature 81. Also before installing the unit they had taken all the measurements of the house, and windows, to assess which AC has to be installed. Please suggest what to do and what might be wrong.

With the vent temp at 55, you may be having too much solar load, poor insulation, single pane windows and air leaks. If the house cools down at night you need to address some of the issues noted above. Where do you live and what is the average high in the last couple of days?

Sounds like a undersized ac unit. Or very poor ductwork