Furnace Control Board ST9120U For Honeywell Furnace Control Board ST9120U. Universal wiring harnesses included for simplified field installation LED indicators provide status and diagnostic information for faster troubleshooting Fan on/off delay settings field-configurable through dip switches Replaces 41 existing Honeywell Resideo controls This circuit board had been installed in a gas furnace in December of 2021 and removed in good working condition in December 2022. Furnace was replaced due to heat exchanger.