This is a BRAND NEW Lennox/Armstrong/Ducane Defrost Control Circuit Board. The Part # is 84W88 (also 84W8801). Honeywell part # is 1084-851 (also 1084-83-8513A) Thanks for looking and good luck!
The control board is the "brain" of your unit, coordinating and executing the operation of other various components by sending voltage when and where needed. A control board is constantly monitoring sensors and safety switches in the unit.