I bought a brand new pro neb ultra 2 from ebay. It worked fine for like 3 months, then all of a sudden it would push air, but not nebulize my meds (wouldn't mist them, though it was pushing air fine). I thought it was the neb cups going bad, so I got brand new cups. Still same thing. I hooked up my ancient compressor and it misted just fine. No clue what could have gone bad.