I have a Carrier unit in a two zone configuration. The system was installed when the house was built ten years ago. To date, the system has functioned perfectly with only minor and routine maintenance issues. The first zone supplies the first floor, and the second zone supplies the basement. Each zone has its own Honeywell thermostat. All of the ductwork is in an unfinished area of the basement. The main duct that supplies the first floor has an electronic damper, as does the main duct that supplies the basement. When the first floor thermostat calls the system to cool, the unit properly supplies cool air through the diffusers on the first floor. Because the basement is cool already, the basement thermostat is not calling and the basement zone should not be blowing cold air. In my system, though, after about two to three minutes, the basement zone damper opens, and cold air flows to the basement. This has two undesired effects – the basement becomes too cold, and the first floor does not cool as efficiently as it should (since air is now being allowed to flow into the basement). In addition, there is a duct sensor that is in place in the first floor ductwork, and wired to the control board. I had a Carrier dealer service man look at the system and he could not find the source of the problem. He concluded that the basement thermostat may be bad, but he did not change it. Several years ago, a non-Carrier service man told me that one of the dampers was “reversed” and he made a change. Any help or advice would be greatly appreciated. Thank you.