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Air Compressor Motor Humming

the_nelson

Member
Joined
Jan 21, 2015
Messages
23
Location
The Union
Greetings from Northern California!

I am relatively new to air compressors. Have always used a small pancake style one for my projects. Our business moved into a new warehouse and for the first time, I actually have shop space. With this came the idea to get a larger compressor.

I mostly use nail guns and pneumatic rivet guns. Have no real use for any other air tools and do not have any 220V close to where I needed to put the compressor, so I went with a Kobalt 2-HP 30-Gallon 155 PSI 120V compressor. Was able to combine some coupons and hit a sale, so I walked out of the store with it for $300.

Being that I have the shop space, I wanted to install air lines and drops around my shop area. I went with the RapidAir Maxline kit in 3/4” and just finished getting it installed. Went together very easily and I made the suggested jig to straighten the hose. Came out pretty well.

I just fired up the system for the first time and checked all of my fittings for leaks, then waited for the compressor to start up and refill the tank. This is where my problem starts. The motor hums and does not turn over.

Here is a basic schematic. I have a 120V 20A outlet that the compressor is connected to. Coming out of the compressor, I have a ball valve and a 1/4” to 1/2” bushing that connects via a 3’ 1/2” hose to a Pneumatic Plus Air Filter / Regulator combo with 1/2” NPT. From the regulator, I have 3/4” fitting that connects to the 3/4” Maxline. First drop is roughly 40’ from the compressor and the entire system is roughly 85’.

The tank will fill to 150 PSI and everything is fine. Once it drops to 75PSI or so and the motor kicks in, it hums and eventually blows the breaker. In order for me to get the motor to run, I have to manually drain the tank to 25 PSI.

You will have to excuse my lack of knowledge when it comes to air compressors. I have the basic idea down, but I’m a little stuck right now.

I removed the Kobalt regulator and went with the ball valve instead. Could that be the problem?

I am seeing 121 V at the outlet, so I'm assuming this is not power. From what I have read on the internet, it seems as though it is excessive pressure and trapping air over the piston??

Appreciate any help any of you guys would offer!!

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the_nelson

Member
Joined
Jan 21, 2015
Messages
23
Location
The Union
Not the start cap. Metered it and all is well. When the tank gets down to 25 PSI, the motor turns over and fills.

I think I've narrowed it down to the unloader valve. Trying to warranty one right now.

Thanks for the idea though!
 
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redmondjp

Well-known member
Joined
Nov 25, 2014
Messages
2,318
Location
Redmond, WA
+1 on the unloader - do you hear a brief hissing sound when the compressor first
shuts off? You should; that is the sound of the unloader doing its job. Search on this site and you will find all of the information you need on that topic.

/snark on: if you motor is just humming, you need to teach it the words!
 
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