Before you decide to turn on that A/C, check to see if your windows are opened properly! Sounds crazy but most people are opening their double hung windows wrong.
Don't just grab the bottom sash and open it all the way... what you need to do it open the top section down some AND the bottom section up some. The reason is that the cooler air will come in through the bottom opening and exhaust the hot air trapped up at the ceiling of the room through the upper area. A very simple principal and one that just may keep you from jumping to the thermostat a little bit longer.