The York S1-031-03498-001 Demand Defrost Control Board senses temperature and when defrosting is needed based on temperature sensor inputs, and engages the defrost control relay. This control board is only for use with York HVAC. For an efficient and reliable HVAC system, the York Demand Defrost Control Board senses temperature and when defrosting is a great choice for optimal syst... https://www.partshnc.com/york-s1-031-03498-001-demand-defrost-control-board