Thanks for the post!

Typically if the pump is forcing air out of the Inlet instead of sucking air in from the inlet, it's due to faulty/defective reed valves in the pump.

I would remove the pump head and inspect the two rectangular reed valves...they're probably either rusted, cracked or disheveled so that they're not resting on the valve plate in the correct position.

You can put a very light coat of Vaseline on the edges of the valves to keep them in place on the valve plate when you re-install them.

There's a chance you'll just need to throw in a valve kit, which typically includes Gaskets as well.

You can find the parts for this unit (Type 1) by clicking on the below link:

www.mastertoolrepair.com/air-compressor-...-d55150-p-21200.html

- MTR