Compressor problems

[smooth72]

I have a 5hp 60 gal Sanborn upright. When it cycles on it starts fine and run for a few minutes, then it starts bogging down and gradually slows down then it pick back up till it runs normal till it airs up. Any idea what would cause the bogging?

 

[Kev442]

Thick, cold oil in the compressor head.

 

[rickycobra]

It could be that it needs time to warm up just a bit. Around how old is it?

 

[smooth72]

It is in a heated garage, it is about 15 years old. The Strange part is that it runs fine for 5 to 6 minutes before it bogs down for about 5 min. then runs normal.

 

[Zeke]

That's an unusual problem. Sometimes they bog down when the voltage is not high enough for when the load starts to build. But, in that circumstance, they usually don't come back. It could be loose belts that grab better when the unit gets warmed up.

I do have a jobsite unit that needs a 20 amp 12 ga circuit or I have to run it for a few minutes with the drain valve open. Once warm, it will run on a 15 amp 14 ga house circuit.

But, it won't first start up, then bog and then finally run like yours.

 

[e-tek]

It can only be two things:
1. surges in power - is anything else running when it happens?
2. the check-valve that lets air in from motor, but not out - could be stuck.

 

[nehog]

Does the motor have both a start and a run capacitor? If yes (mine does, for example) then possibly the run capacitor is failing.