I've been having some trouble with the central AC in a house that I just recently moved into. The problem is, the AC works fine, but it won't keep a constant temperature. Basically, when I turn the thermostat to "cool" and "auto" it just runs and runs even after the desired temperature is met. I thought that it might be a bad thermostat, and since I wanted to upgrade to a programmable one anyway, I bought a new thermostat (Honeywell CT3500A1004) and installed it. The AC still does the same thing, I set the temperature at one day 75 when I left for work and when I got home it was down to 68 and the AC was still running. Now I haven't been running my AC during the day, but when I get home the temperature in the house is over 80, so it takes almost the entire night to get it back to a comfortable level. This is my last ditch effort before I have someone come out, any suggestions?