Similar "bolt not retracting" problem

pin has debris /bent and needs lube or retractor needs repair

1) Check to see if the drive belt is intact
2) Check and make sure the driver blade is not bent
3) Make sure return device is properly clipped down so the driver can fully retract
If you don't have success, please let me know more details of what the tool is doing and I will try to talk you through it.

Normally I would say you aren't using enough air pressure because somewhere around 80psi (every tool is different) will not be enough to fully retract the driver. At 110 you are fine so that is not the case. I doubt it is broken because a broken driver will still retract unless it broke near the piston. My guess is it needs the o-rings replaced but you can pull the top head and pull the driver out first to make sure. Parts and breakdowns can be found here as DeWalt owns Porter Cable.

PC FR350 diagram

Which model is it? What happens when you try and shoot it? Is it leaking air and if so from where? Is there a nail jammed in the tool?

Most likely there is a problem with swollen orings between the cylinder and cylinder spacer (white plastic piece between cylinder and body ). Order the oring kit because nost likely when you take the gun apart the orings will fall apart. Dewalt used vinyl orings instead of viton on critical areas of the cylinder and these vinyl orings failed.

Are you using a few drops of air tool oil in the air inlet before every use? If ok, then there may be water or debris entering the air line in some fashion that is causing the valves to stick. Hope this helps!

Increase air pressure.... you're way too low......

Go to eReplacementParts.com : Power Tool Parts and Tool Repair and find a diagram and the parts you need.

if its new warranty it,
otherwise all it should need is a rebuild kit . its just a bunch of orings and gaskets. pretty easy to do. take some pictures as you take it apart to help with reassembly.
Dewalt should have scematics online or ereplacements.com

Check whether the trigger is working properly, and whether the air valve is not leaking.