60 gal air compressor bogs down

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RegularGuy

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Hi Everyone!

I have a 2005, 60 gal., single stage, 7ph (peak), belt drive, Sanborn air compressor which is wired directly to the breaker box by a short piece of romex wire. It has performed well for 16 years until recently, receiving regular but modest use. All parts are original. Model LA7006056.

In recent months it performed fine at start up but then the motor slows down and has a lower, labored sound when the pressure is roughly 60psi, although the compressor did still go to its usual maximum (120psi or so) but perhaps more slowly than when the compressor was newer. Then last Saturday, it began sounding labored when the pressure built up to 30psi or so, and did not go beyond about 70 psi, although it continued to run while sounding labored.

If I open the tank’s petcock at the bottom of the tank, it runs fine and continues pumping air into the tank (which then leaks out the open petcock).

Help please.
 

bud16415

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The electric motor is getting weak or the compressor is starting to show signs of binding up. I would take the belt off and turn the compressor over by hand with the drain valve open and also closed to get a feel if it is binding. Does the crankcase have a place where you add oil? Have you checked it or added any over the years? Also turn the motor shaft by hand to see if maybe it is dragging with bad bearing.

The fact that it is still making and holding pressure tells me the top end is likely not the problem.
 

oldognewtrick

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Also check the air filter, if equipped, to see if it's clogged with dust.
 

RegularGuy

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Thanks, Olddog! I did check the air filter. It needed a clean (which I gave it) but then I tried the compressor again and the problem did not change.

Bud, thanks for your help too. The only place to add oil is already at the proper level and was changed a few months ago. I grabbed the belt pulley by hand and turned it over. It seemed to turn freely with what seemed to be the resistence I would expect given the fact that I was turning the other pulley too and hand-turning the compressor also.

Further thoughts please, Bud and Olddog, or anyone?

Thank you in advance!
 

oldognewtrick

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Does it have a start and run capacitor? There will be a bump or two on top of the motor.
 

oldognewtrick

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Sounds like it might be ready to replace the capacitors. I have a start capicator on my 60 gal tank that's fussy to start, been to lazy to go to Granger and replace it.
 

oldognewtrick

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If you are not familiar with a capicator, watch some YouTube videos on how to properly handle them. They store a LOT of energy and can hurt you if mishandled.
 

havasu

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If you are not familiar with a capicator, watch some YouTube videos on how to properly handle them. They store a LOT of energy and can hurt you if mishandled.
So, I guess using my tongue to determine how much energy is left, like I do a 9v battery, is not recommended?
 

RegularGuy

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Thanks, Olddog. I did watch some y-tube videos. In the pdf image, the bump (capacitor) on the left is smaller and seemed to do what it is supposed to do when I tested it with my multimeter. (I don't have a micro-ferads tester.)

When I used my analog ohms tester on the capacitor on the right (see clip image below, to which the blue line is pointing) the tester's needle went all of the way to the right and stayed there. I think this is the run capacitor and that it did not act how it should in the test.

1633097388264.png
By contrast, when I tested the smaller capacitor on the left, my analog ohms tester's needle went all of the way to the right and then started to go back to zero.

Does that sound like a bad run capacitor (the one on the right in the picture)?

Thank you for your thoughts!
 

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Eddie_T

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I don't recall (too many years ago) the symptoms but I had a shallow well pump that the centrifugal switch failed to open the start capacitor circuit.
 

RegularGuy

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Hmmmm. Thanks, Eddie. I will have to consider how that applies. I am a beginner...
 

mikeemike

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I had a compressor run sluggishly but only when plugged into an outlet that was far from the main panel in my house. There was enough of a voltage drop to affect performance in my case. Obviously you have a short run there, but it might not hurt to try a heavier piece of romex or maybe a different spot on the breaker box, just to ensure voltage drop isn't an issue.
 

BuzzLOL

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Probably should invest the $30-40 in a VOM that also reads capacitor capacitance... it's also handy for A/C compressor capacitors which is usually what goes wrong with A/C as well...
I wish I would have went $20 more and got the oscilliscope function as well for working on vehicle fuel injection...
Another common air compressor problem is motor runs fine but little or no air pressure when reed valve in compressor head breaks off... might even fall into compressor and keep it from spinning over...
 

Blue Jay

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Yes the run capacitor is bad from the readings gave, it should go back as the other one did.
 

DesertRider

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Question... was it running fine before the problem surfaced? If so then the wiring is fine... IMHO just replace both caps, and you should be fine... in my experience if one goes south, the other is not far behind. Good luck

BTW... how’s the oil in the compressor? In the sight glass or on the indicator cap? Low oil could cause a bogging down too
 

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