How to fit Duplexer unit HP 4250

Hi Mary L,
Good day... This steps may be helpful for you. try sorting one by one steps...below
solution 1:
1.The duplexer side adjust has failed.
2. Turn the printer off and then on.
3. Reseat the duplexer assembly.
4. Replace the duplexer assembly.

solution 2:
1. The duplex printing unit is not functioning.
2. Turn the MFP off, and then turn the MFP on.
3.Reseat the duplexer.
4. Check the connection between the duplexer and the DC Controller.
5. Replace the duplexer.

solution 3:
1. Duplex mechanism failure.
2. Duplex slide adjust has failed.
3. Temporary error.

Hope this solve the problem...
Thanks in Advance.
Hp Error Code 69 Service Errors 69 Printer Repair Message

You've done everything I would have done and more.
How about you installing a DOA duplexer. At this point I would change it again. Is there another printer that you can swap duplexers with?
There is a paper path sensor test (letter H) and manual sensor test . I don't know if the Component test checks the duplexer, but you should be able to find out.
Is the printer still under warranty? Can you call HP or are you an HP tech and you can call 2nd level support.
Just a thought....when you run a Config sheet, does it show the duplexer?

If that's the access foor at the back of the printer might just be loose or unlocked. Try locking the door into place and see what happens. Or if you have a duplexer. Try these:

1. Press the buttons on each side of the duplexer to release it. Figure 7: Press the buttons to release the duplexer
2. Remove the duplexer from the product.
3. Reattach the duplexer. Press the buttons on each side of the duplexer, and then gently push the duplexer back into the rear of the product until it snaps firmly into place. Figure 8: Reattach the duplexer
4. Repeat the steps to reattach the duplexer if the lights remain on.
   Link: HP Deskjet 940c Printer - Blinking Lights

As you face the printer, walk around to the left side. You will see the power switch. Above the power switch is the duplexer. It pulls out.
You said the duplexer is jammed, so you might not be able to pull it out.

Is the duplexer jammed or is there paper jammed in the duplexer?

After you attach the two-sided printing accessory (duplexer) to your product, you do not have the option to print on both sides of the paper when you try to print. The two-sided printing option is not available in the print dialog box.
NOTE: The HP Automatic Two-sided Printing Accessory (Duplexer) ships with some printer models and is available as an optional accessory for others. Solution First, choose your operating system. Next, follow the steps to make sure that your printer driver recognizes the duplexer. Show all ' Hide all Windows XP Follow these steps to make sure that your printer driver recognizes the duplexer. Step one: Add the Duplex Unit to your printer settings

1. Click Start , click Control Panel , and then click Printers and Faxes .
2. Right-click the printer icon ( ) for your HP product.
3. Click Properties , and then click the Device Settings tab.
4. Click the plus sign (+ ) next to Installable Options to expand the list.
5. Click Duplex Unit (for two-sided printing) , and then select Installed from the drop-down list.
6. Click Apply , and then click OK .

Step two: Set the Two-sided printing preference

1. Click Start , click Control Panel , and then click Printers and Faxes .
2. Right-click the printer icon ( ) for your HP product.
3. Click Printing Preferences , and then click the Features tab.
4. In the Paper Saving Options area, select Automatic from the Two-sided printing drop-down list.
5. Adjust other print settings as needed.
6. Click OK to save the settings.

Windows Vista Follow these steps to make sure that your printer driver recognizes the duplexer. Step one: Add the Duplex Unit to your printer settings

1. On the Windows taskbar, click the Windows icon ( ), and then click Printers .
2. Right-click the printer icon ( ) for your HP product.
3. Click Properties , and then click the Device Settings tab.
4. Click the plus sign (+ ) next to Installable Options to expand the list.
5. Click Duplex Unit (for two-sided printing) , and then select Installed from the drop-down list.
6. Click Apply , and then click OK .

Step two: Set the Two-sided printing preference

1. On the Windows taskbar, click the Windows icon ( ), and then click Printers .
2. Right-click the printer icon ( ) for your HP product.
3. Click Printing Preferences , and then click the Features tab.
4. In the Paper Saving Options area, select Automatic from the Two-sided printing drop-down list.
5. Adjust other print settings as needed.
6. Click OK to save your settings.

Windows 7

What is the code? This unit does not have a fan in the duplexer nor for the duplexer. The 9500 has a fan housing but there was never a fan put in by the design team. Give the code and I look it up to see the problem.

Face the back of the printer.
Pull the duplexer back about 4 inches.. There on the left side is an opening with 3 small flat metal pieces sticking out. One end of the power cord has 3 flat pieces of metal sticking out. Use the other end to plug into that opening on the printer.
Push the duplexer back in. Now take the other end of the power cord, the male end, and find a thing on the wall in your room that this male part can fit into. It's usually about a foot of the floor. Let's call this an OUTLET. It may take you a couple of tries, but I have confidence that it shouldn't take you long to fit the end of the power cord into this thing that we call an outlet. Goodluck.

If it's the right duplexer you just remove the back door and replace it with the duplexer. There are buttons on each side to push to remove or install. If the size is not correct you don't have the right unit for your machine.

If you really have an HP 4350dtn (d = duplexer), then the duplexer is not connected correctly. Look at the back of the printer for the duplexer. It prtrudes from the back drop down tray and is used to print on both sides. I would pull it out and push it back in to make sure all connections are tight.

Tray number 1 is the manual feed tray in the front of the unit.

First, the machine always prints the first page first. Make sure you have the right driver (4 plus and not 4)and check the settings in the device settings of your printer driver on the pc. Also make sure the duplex unit is for the 4 plus and not the 4.