If your printer supports duplex printing, this VBA code will turn off or on duplex printing from within an Access database.
To turn duplex printing on:
Dim prt As Printer
Set prt = Application.Printer
With prt
.Duplex = acPRDPVertical
End With
To turn duplex printing off:
Dim prt As Printer
Set prt = Application.Printer
With prt
.Duplex = acPRDPSimplex
End With