My central AC unit has stopped keeping the house cool. I checked the filter and it is clean. The outside part of the system is also functioning. I did notice that there was some water building up on the floor around the bottom of the system. Also, the insulated copper tube appears to be sweating; I never noticed that before. The house thermostat is set for 72 degrees, but it is reading 80 degrees and rising. Please help me and thank you.