I recently change out the fan unit on my furnace but I must have wired it wrong. The problem is in the summer I can run the A/C on auto, but the heat side only runs when the fan is switched on.
Did I miss a relay wire or overlooked it all together?
Trying to conserve energy. Thanks!

The heating uses a separate winding and relay for a lower speed for the blower than fan on and cooling. For maximum efficiency and comfort, you need to carefully select a fan speed to give the proper temperature rise. If the new blower is identical to the old one, you need to identify the leads that were connected to the control board and connect them the same place. If it is just one that could work, or you didn't record the old connections, you may need a technician to hook it up right. Look at it. It could be as simple as spotting a plug and snapping it into its spot on the board.