Does closing the vents in rooms not being used, increase the resulting air flow into the rooms with the vents opened? I am trying to cool or heat rooms that are only being used.
Closing a vent should divert more air to the other open vents. The layout of the duct work will influence how well this would work.
This is no harm in experimenting. Turn the fan to the on position at the thermostat. Close a vent and see how it affects the other rooms. Keep experimenting to get the combination you want. You man find the additional air rushing through the open vents many be too noisy.