I just bought a brand new house with brand new American Standard air conditioner. It seems that when I try to set a lower temperature than the current temp, say, current is 78, and I set it to 76, then it started to run for somewhat long time to reach the set temp of 76, usually it needs an hour or so, but then, after the thermostat already shows the set temp of 76, it still continues to run even longer hours, usually 3 to 4 hours before it can stop for the first time. I understand that when the thermostat shows 76, it is probably at higher end of 76, say, 76.9, and the system continues to cool the house until it reaches the lower end of 76, say, 76.1 or 76.2. But what is causing such long hours of continuous running after thermostat reads 76? It should not take 4 hours to reduce temperature from say, 76.9 to 76.1. What could be the problem with the air conditioner?

Thanks for your help in advance!

There is a cut-off switch that stops the action when the temperature falls to a certain temperature. The range is usually 3 - 5 degrees. Evidently, the switch is malfunctioning and the action goes on longer than necessary when the range of difference is met.
The dealer who sold you the unit... or the manufacturer could be got in touch with and service dealt with.

If it is a digital thermostat the overlap or run time might be adjustable. Usually this is not a user friendly setting to adjust. If you have your instruction manual from the install it will be contained in there. If the people that put your equipment in did not leave it I would demand they get one and also the books for all your new equipment. All manuals state to leave for the homeowner. If no luck Call the building department that did the inspections on your new home and ask them why they do not enforce the code for leaving all the manuals at site.

Air condition is running non stop and will not cool house until around 3am its 11 and still 85 in house only small amt of air blowing from vent antifreeze just put in last month what could be problem