I have both an HP Laserjet 4 and an HP Laserjet 4 Plus printers, both equipped with plug-in HP Jet Direct cards for network use. In addition, I have two HP duplexer units.
This morning, I tried setting up one of the duplexers with the 4 Plus printer. I first went offline, then used the Menu screen on the lower level of keys to access the printer menu. There, I set up Duplexer=On as the default, then went back online.
Then I tested this about three successive times with a two-page document from our network connection. Each time, it printed the letter on two separate sheets, one side only, and ignoring the duplexer.
What have I missed here? Should I reconfigure the HP Jet Card as well? How can I tell how much memory is onboard the printer? Etc.