single zoning system in the house,, the upstairs was always cold even if the thermostat is off,, they can still feel air coming out of the upstair vents. We stated diagnostic at the indoor unit ,,, there is a Honeywell zoning control board,, set to cool one thermostat at a time, checked voltage needed on each zone, both zones are getting the right voltage, highly believe the electric damper that cools the upstairs is stuck open ,,,measured temperature differential and noticed there’s always airflow coming to the upstairs . Will send estimates for recommendations.
