One more thing, depending on what type of heat you have, It might be as simple as adding a simple fan relay or at most a sequencer to take the place of the board........Really kind of a waste of money to replace the board if you are gonna change out system in the near future.

Also did you check the G terminal where the tstat wires terminate to the board..........most likley on your unit the heat controls the fan operation and in cool the tstat controls the fan......... meaning you need to have 24v between common and the G terminal to energize the fan relay in cooling