I live in houston. I have lived in this house for approx 3 years. I noticed last year that my A/C was running all day long. It was toward the end of summer and I had it charged. Dont remember was it was charged to. Now this summer its doing the same thing. When the temp outside gets to the high 80's my A/C keeps going. I also remember installing a digital thermostat last year. Could this be a problem. It reads the correct house temp on its display. I ask about the thermo because my system is supposed to be a dual speed and wonder if it affected it somehow. The thermostat that was in the house was a old POS anyway. just a turn dial type. I am told that I have a 3 ton unit. Rheem/ criterion gas furnace upstairs. Tempstar 2400 outside. House is approx 1800 sq ft. The temp drop is pretty good out of the registers. Attic is pretty well insulated. Coil looks clean. the return air sucks pretty good. I can close the door to the farthest room in the house and feel the air get sucked from under the door. Any help or idead would be appreciated.