I replaced control board on furnace and now blower fan will not come on when air compressor comes on.

You say blower fan , is this the fan in the furnace or in the outdoor unit?

It sounds like you didn't get the blower motor wires put back on the correct terminals on the control board. Brand of furnace? Terminals on the board. i.e. fan, heat, cool, park, neutral or circ/neutral? Yellow/low voltage wire from 'stat tied into Y terminal on board with one of the wires to the outside unit? Are you sure that connection is good and secure?