Hi, We recently had a 3 1/2 ton American Standred 12 Seer heat pump put in. It has a white-rogers heating-cooling digital thermostat. Problem: Heat pump goes on and off every 4-15 minutes, even though the house tempture and set tempture are the same. If its colder, less than 40 degrees, it happens every 4-5 minutes. 50 degree plus every 15 minutes or so. We can stop it by manuel dropping the set tempeture below the house indicated tempeture. When the HP is running early in the morning heating the house from night temp to warmer morning wakeup temp and it meets the programed wakeup morning temp it continues running for 15 more minutes, instead of shutting off. Our installer is working hard to figure out the problem. They changed the termostat, replaced circut boards, but no fix. They are throwing around the idea of "static pressure" because the HP was sized up a half ton in anticiation of the addition of a bedroom. Any ideas on whats wrong?

Thanks for any imput.