Hello Bill, I have a Campbell Hausfeld VT629002AJ – 20 gallon oil type air compressor that has had an issue for a long while now and I am trying to sort it out. The compressor will start from empty and fill all the way no problem, but has a hard time starting when it tries to kick on as the tank is being drained.

When it does fill to cut out I can hear a loud hiss from the unloader valve (so I assume it is working) also when partially full I can hand turn the pulley and hear air escaping from the valve… I did replace the check valve, but that has had no effect. at this point I am wondering if it could be the electric motor? Thanks in advance for any insight you could give. Jordan B.

Campbell Hausfeld 20 Gallon Air Compressor (VT6290) Photo: campbellhausfeld.com
Campbell Hausfeld 20 Gallon Air Compressor (VT6290)
Photo: campbellhausfeld.com


Hey Jordan. Yup, it sure sounds like your unloader valve is working OK and that lets out the first and most common reason why an air compressor will not start when there is air in the tank.

What’s next? There’s a page link on the troubleshooting page about compressors that won’t restart when the air is being used, and I believe your answer and much more info will there.

Meantime, I suggest you visit the page on this site about how check the motor capacitor(s). I suspect that a failing or failed capacitor is the main issue.

If the compressor was working properly before, and you haven’t relocated it to a new power supply, that is.

There may be other issues but these are the main two. Check out the cap, and give us an update as to what you found if you would. Thanks.


Doug from s.d.ca posts… can you tell if your machine was made before or after 2001? It may not matter if your motor capacitor is bad, but may if the cap is good. Please let us know.