Thanks for the post!

It could be a couple of things here...

MOST likely the problem is that the motor's Belt is broken off.

The next most likely reason for this is that one (or more) of the Reed Valves in the pump head are damaged or have fallen out, or that the Piston (compression) Ring around the Piston is damaged.

You can view a full breakdown of this air compressor with a parts list by clicking on the below link:

www.mastertoolrepair.com/air-compressor-...6-155839-p-6499.html

I would take the shroud off of the unit and look at the Belt: is it frayed or torn? If so, this is your problem.

If not, then take the pump Head off and look at the small, flat reed valves that are riveted or bolted onto the Valve Plate; are they all there? There should be one on each side of the Valve Plate (the Intake Valve and Exhaust Valve). If they're damaged or missing, then you need to replace the Valve Plate Assy (if available...it may be obsolete, unfortunately).

If the Valves are in good shape, next check your Piston Ring. Is it damaged? Is it torn or nicked around the edges? Is there a tight seal with the inside of the Cylinder wall? If not, you need to replace the Piston/Cylinder.

Take a look at the above and feel free to reply with what you find. If you still have questions, let me know and we can narrow it down further for you.

- MTR