Why is only air comes out of Nail gun of Porter Cable DA250A?

did u get the broken nail head out of the gun?

The part that you are looking for is most likely the "piston stop."
this part can be found at Dewalt service centers as they own Porter Cable. Also some Ridgid nail guns use the exact same parts as Porter Cable. Good luck with your repair.

Nail Gun Not Firing Repair
How To Diagnose An Air Nailer

Are you depressing the nose of the nail gun against the material to be nailed first? Without doing this, the trigger will not "unlock". You can read a pretty in-depth review of this nail gun at OnlineToolReviews com Porter Cable FR350A Full Round Head Framing... which might also help.

Easy to fix. Remove the head and pull out the cylinder. Look for black band around lower part of cylinder. This band (check band)should be placed around series of small holes. Replace if broken with any rubber that will hold up in oil or use a bunch of orings to fill space. Good luck.

The manual for your gun specifies 34-degree nails from 2 to 3 1/2 inches long. 28-degree, wire collated nails are a Stanley-Bostitch thing and they only work in their nail guns, they will not work in your nail gun. You need 34-degree, paper-tape collated nails. I know Senco framing nails will work in your gun and I think Duo-fast makes 34-drgree nails but check that before buying them.

Eighter one of these will work good for nail guns personaly i have the porter cable and i like it i do a lot of construction work. And i think the porter cable comes a finish nail gun for small nails and staples mind did. But there not for running tools that require a large volume of air like air sanders air rachats or air cutters.

check the magazine bolts are tight and that the magazine is snug aginst the nose. also be sure you are using 16 gage brads and not 18 gage

You have to oil the nailer with pneumatic oil, or you're using the wrong size nail

I've had to remove the plate over the "firing pin" a couple of times (the allen wrenches come with the gun) to release it. Mine was caused by a bent pin, that happened when I hit the hose and knocked it off the bench.

When I finally replaced it (CPO/Porter Cable), it's been fine ever since.