1) Make sure that the HP printer that your are using will support a duplex unit assembly.
2) Turn power off to the printer and unplug all cables from the rear of the printer.
3) Remove the rear dust cover. The duplex unit assembly will be installed through the back of the printer.
4) Once you install the duplex unit, turn on the printer and wait until it warms up and goes online.
5) Once the printer is ready, you can run a self test or test a page through the maintenance panel located on the top front area of the printer.
6) You can set the Duplex option on the maintainance panel to "Duplex = NO" or "Duplex = Yes". You can also select the Duplex option on the printer driver Properties selection.
7) Test the printer.
The duplexing unit will function correctly.