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Sick Air Compressor


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#1 LilysDad OFFLINE  

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Posted April 17, 2015 - 04:37 PM

I have a 2hp 20 gal compressor that I need help with. It starts just fine when it's empty, but once it's full and shuts off and it drains down aways, it won't start again. The motor just hums. If I drain it all the way down, it will start again. The pressure gauge is fine. Could this be the capacitor?


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#2 crittersf1 OFFLINE  

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Posted April 17, 2015 - 04:42 PM

Yes it could.


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#3 boyscout862 OFFLINE  

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Posted April 17, 2015 - 04:43 PM

I have found that the points that work with the condensor will corrode. Becareful with capacitors, they can bite. Clean the points then try it. If that doesn't work it probaby is the condensor. Surplus center has a good assortment of them. Good Luck, Rick

Edited by boyscout862, April 17, 2015 - 04:43 PM.

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#4 Bruce Dorsi OFFLINE  

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Posted April 17, 2015 - 04:49 PM

Most compressors have a check valve to prevent the tank pressure from backing up into the compressor when the compressor shuts off.

 

There is also usually an unloader to relieve any pressure in the compressor after it shuts off.  ...This unloader is often built into the pressure switch, but it may be a separate item.

 

If the pressure is not relieved in the compressor before starting, the motor will often "hum," but not start.

 

As already said, a faulty start switch or bad capacitor could also be the problem, if so equipped.


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#5 LilysDad OFFLINE  

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Posted April 17, 2015 - 05:12 PM

There is a 1/4" pressure line that runs to the pressure switch and attaches to what seems to an air powered solenoid. Would this be the 'unloader'?



#6 Bruce Dorsi OFFLINE  

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Posted April 17, 2015 - 05:28 PM

Quite possibly.   ...Can you post a pic?

 

Is the pressure switch a Square D "black box?" 



#7 Auburn David OFFLINE  

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Posted April 17, 2015 - 06:13 PM

Mine did that and drove me nuts..turned out I had it plugged into an extension cord that had degraded over time.



#8 Sawdust OFFLINE  

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Posted April 17, 2015 - 06:20 PM

Like Auburn Dave mentioned check that first the most easy to fix. One of my job site compressors will do this if it's not plugged into a 20 amp receptacle or not the right extension cord will do this too as mentioned.
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#9 olcowhand OFFLINE  

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Posted April 17, 2015 - 06:25 PM

Sounds like the guys have covered all possibilities.  


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#10 Username OFFLINE  

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Posted April 17, 2015 - 06:30 PM

You should be able to hear the air bleed off when the it shuts off it the unloader is working correctly.



#11 LilysDad OFFLINE  

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Posted April 17, 2015 - 06:30 PM

Quite possibly.   ...Can you post a pic?

 

Is the pressure switch a Square D "black box?" 

I'll get a picture tomorrow.



#12 ol' stonebreaker OFFLINE  

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Posted April 17, 2015 - 09:28 PM

  If it's the check valve the unloader will leak continuously until the motor tries to start again.

                                            Mike



#13 LilysDad OFFLINE  

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Posted April 18, 2015 - 09:29 AM

air comp1.jpg air comp 2.jpg air comp 3.jpg air comp 5.jpg air comp 6.jpg air comp final.jpg Here are some pics.



#14 LilysDad OFFLINE  

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Posted April 18, 2015 - 09:38 AM

You should be able to hear the air bleed off when the it shuts off it the unloader is working correctly.

 

 

  If it's the check valve the unloader will leak continuously until the motor tries to start again.

                                            Mike

Are these conflicting statements?



#15 ol' stonebreaker OFFLINE  

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Posted April 18, 2015 - 09:57 AM

  No, if the check valve is working properly, the unloader will only bleed off air between the check valve and comp head, so it's not trying to start against tank pressure. If the check valve is leaking, you'll hear air out of the unloader until the switch closes to start the next cycle at which time the unloader is closed. It sounds like a capacitor or points problem to me. If you have it plugged in where it worked fine before, then that rules out too small a cord.

                                         Mike






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