Do you have gauges? Write down the following on a grid High side, low side, Ambient temp out side, temp coming out of the condenser, temp at intake in the house, temp coming out of the vent. Chart this over time. I bet you will see your pressures climb. Watch the high side to see if it moves back and forth a few PSI... This is an indication that the expansion valve is working (opening and closing). If the system has too much pressure it will cool at first and gradually cool less as the pressures go up. An over charged system is ineffective.

When you get the pressures charted post the grid on here.