Thanks for the post jimbo,

Typically, when the unit will run and not build any pressure (or very little pressure as in this case), it's due to one of the below:

1. There is a major leak somewhere: check all air fittings and connections
2. There is an internal pump problem.

Most likely, the problem lies in the pump...either the reed valves in the head or the piston (compression) ring and cylinder are worn out, not allowing the unit to compress air.

I would turn the unit off, unplug it and remove the pump head. Make sure the metal reed valves in the valve plate are not broken or rusted to the valve plate. The valves should have some spring action to them, which you can tell by gently lifting them up or pushing down on them.

My bet is on the piston ring and cylinder being worn out, as this is a very common problem after some time, especially for older units. The Teflon-coated piston ring probably has a notch, kink or tear along the outer perimeter, now allowing it to seal tightly within the cylinder cup's wall; most likely the cylinder cup is worn pretty badly as well. If you can see light between the piston ring and the I.D. of the cylinder cup, you need to replace the cylinder and piston ring. Parts are probably available, and I can give you part numbers and a cost if you can reply with the model# of the unit.

Hope this helps!

- MTR