My craftsman 12v air inflator model 75114 does not have any air; the motor still runs but has a rattling sound.

SOURCE: Air compressor won't build pressure

If this unit has what appears to be a pipe with fins on it , you may have a ruptured inter-cooler which will be leaking where you stated.

SOURCE: My craftsman air compressor model 919 16737 1.1 hp

Probably the check valve has failed. It apparently is where the pipe goes into the tank from the compressor.

SOURCE: I have a Craftsman 1 hp, 3 gal air compressor

Remove the air filter and see if the inlet is sucking air if so the unit is pumping,if not the valves could be bad or the piston is broken.

SOURCE: Air compresor Craftsman 921.153101 it

if its belt driven ,unplug it(safety first)remove the belt and try to turn the pump by hand.if the pump turn plug it back without the belt. and try it .if the motor doesnt run.check the contacts on your pressure switch.if they are ok and try again.if not you need a new motor.if the motor ,the pressure switch contacts,and the pump are fine.put the belt back back on bleed your tank to zero with an air gun and try to run it.if it work well till it cuts of check if your bleeder release air.you might have pressure stuck in your pump.the compressor needs to release pressure for a soft start.hope this help!

SOURCE: Craftsman Air Comp. 6 hp oil-less, 33 gal horz. tank - sounds really loud

Sources of noise from craftsman oil free compressors (could be Made by Campbell Hausfeld or Porter Cable) include loose fan, failing bearing/s on the piston rod and housing, failing seal ring on piston, air filter intake and loose motor mounts. With the housing cover off, check the fan blade for cracks or loose screw. Turn motor by hand till the piston is at top of stroke. Examine the cylinder for scratches close to top. If scratched, air is leaking past vinyl ring making noise and causing longer fill time. If everything looks ok, suspect noise coming from bearings. Hard to tell if bearings are failing by looking at them. I have seen many failures of the piston bearing on the crank (fairly easy to change, I use alternator bearing from auto parts ) , however, the bearing in the housing just behind the crank bearing is much harder to replacable. Good luck with your fix-it project.