compressor over pressurises or continues to run after pressure is reached

compressor sits humming and trying to turn the motor instead of cutting out. It is a Ferm nail gun compressor.


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Bill says...

From your comment it sounds like your compressor pumps air OK, gets to and then past the normal cut-out pressure, and at a certain pressure that is higher than the normal cut out, the motor stops rotating and hums...?

That being the case, it seems to me that 1) your pressure switch has certainly failed and you should replace it before using the compressor again and 2) in your case, instead of the pressure in the tank rising until your compressor PRV blows off to reduce critical pressure, your motor hasn't got the oomph to push the pressure past a certain point, and it stalls.

A stalled motor is not a good thing, as they are not built to handle that.

So, not only does it sound like your pressure switch has pooped out, you may be close to having the same thing happen to your motor.

Good luck!

Bill

Comments for compressor over pressurises or continues to run after pressure is reached

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Mar 24, 2015
Compressor won't start
by: Bill

First thing is to check your unloader valve Robert to make sure it works properly.

If it does, and the problem persists, start a new thread and include your compressor model number.

Bill

Mar 24, 2015
Compressor won't start
by: Robert

My compressor start build pressure to 150 cut out and when it has to start again the motor just hum and blow the circuit beaker and don't start until there is no more the 30 psi in it what can I do to fix this

Aug 23, 2011
Check your power supply
by: Anonymous

Sometimes a long extension cord or poor power will prevent a motor from starting. It will sit there and humm, usually popping the reset after a minute or so.

Aug 23, 2010
Humming motor
by: frank

My compressor just hums, it does not pump air, is my compressor motor locked up?

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Not likely. Either the motor's capacitor has failed, the motor itself is failing, the unloader valve isn't working, or there is a mechanical issue.

B.


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Compressor shuts off at 50psi

I have a Husky WL6703 air compressor. It has run great until fust recently. when I turn on the compressor, it will pressure up to 50 psi and cut off.

The manual states that the pressure switch has an eternal breaker and can be reset by turning the power switch to off and let it set for a few minutes.

when I turn it back on it, the motor starts and will pressure up about 5 psi and turn off again.

I have to do this repeatably to get pressure up to 100psi. also the compressor will not turn on when I am using it as pressure drops minimum operating pressure. There are no leaks. Also the unload valve does release a short blast of air when motor turns off. Is this a problem with my pressure switch/

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Bill says...

From what you've said S.Moke, then yes, I would surmise that your pressure switch has failed.

Since it's often one of the lowest cost repair parts for an air compressor, it's a good place to start, with replacing yours with a new one.

Cheers,

Bill

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Apr 18, 2011
Same Problem
by: Kenny

I am having the same problem as S.Moke. My compressor turns on to 50 PSI and shuts off then if I reset the Pressure Switch I can get it to go up another 20 PSI per reset till I get high enough. I also cannot get the motor to start automatically no matter what the pressure is. Do you have a wiring diagram to see how the switch is supposed to be wired? Thanks.

Aug 18, 2010
Not the pressure switch
by: jd0770

I'm having the same issue. I was about to replace the pressure switch also until I threw a voltmeter on the motor and saw that it was getting 120 V even after it shuts off. If it were the pressure switch, it would have cut off this voltage. I'm convinced its the thermal overload protection on the motor. I will be disassembling this weekend to try and by bass it.

Jul 20, 2010
trip or thermal overload
by: Anonymous

I checked wiring and it is correct. I don't know how to tell the difference between a pressure switch trip or thermal overload. All I can tell you is that when it shuts down, I have to turn the pressure switch off and wait a few minutes then turn it back on before the compressor will run. (in the manual this is the instructions for reseting the pressure switch) If I leave the switch in "on" position it will not turn back on no matter how long it sets. But now if I "reset the switch" the compressor will turn on but shut down again after pressuring up 25psi more. I have to go through this process each time before reaching maximum air pressure. Before I started having this problem, this occured maybe 3 times in 4 years and each time the compressor would power on and off like it should after resetting the switch. I am also not having any issues with tripping external breaker for outlet.

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A thermal overload has to do with the motor overheating. See the page on pressure switch for details about them.

Send photos in of your unit ( create a new thread ) and I'll see if I can help you spot the difference.

B.


Jul 19, 2010
bad motor?
by: Anonymous

I will check the wiring on the new pressure switch. There is nothing more I can do. I also replaced the check valve and unloader valve. No leaks. Tank holds pressure. After changing out everything but the motor, the issue is still the same. I find it hard to believe the new pressure switch would have exact problem as the one replaced. I have noticed that the motor gets hot real quick once it starts running. Is that normal? Could I have a motor/pump issue?

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Compressor motors do run hot, but how hot is hot?

What I'm not understanding, and a question I should have asked earlier, is when the unit shuts off at 50 PSI, does the pressure switch trip? Or, does the compressor motor go off on thermal overload, and you have to wait for it to cool before it starts.

If the latter, then my apologies, you may have a motor load / wear issue.

If the pressure switch is tripping, then it's the pressure switch that's the problem, in my opinion.

B.


Jul 16, 2010
replaced pressure switch
by: s.moke

Bill,
I replaced the pressure switch and still have the same exact problem. I do need to clarify that after it shuts off the first time at 50 psi and I turn the switch off and let it set for about a minute and turn back on, it will pressure up in increments of about 20 more psi until it turns off again. And I go through this routine until reaching 125 psi. but it will not cut off and on if I leave the switch on.

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The device that turns the compressor on and off is the pressure switch.

It should allow power to flow through the switch when the pressure falls to the cut in pressure level, and shut off the power flow to the compressor motor when the high pressure cut out is reached.

If the pressure switch trips off at 50 PSI, it's not working properly.

Or, it's not wired properly.


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My compressor builds to exactly 20 lbs. pressure then shuts off

My compressor builds to exactly 20 lbs. pressure then shuts off. It will not turn on again until it reaches 0 lbs. pressure, then I can turn it on and it runs again to 20lbs. The motor sounds fine and it fills quickly, it just will not go above 20lbs.

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Bill says...

Please click the link the the Pressure Switch page from the nav bar.

I think, once you read it, that you will find that it's likely your pressure switch that has somehow failed.

Cheers,

Bill

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Cutting out on restart

hi ive got a atlas conpo compressor the problem i have is from a empty tank it fills fine and cuts out at 120psi when i start using spray gun and compressor drop to 80psi it starts up for about 3 seconds and then cuts out it will only restart if i drop pressure down to 25psi then will refill but same happens again on restart could you help me with this problem please

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Bill says...

What starts the compressor when the pressure drops is the pressure switch.

What stops the compressor motor when the cut out pressure level is reached is the pressure switch.

The pressure switch trips repeatedly as the compressor goes through it's normal cycle, and they do wear out.

Before tackling and further diagnosis on your compressor, I'd look to a problem pressure switch first.

Cheers,

Bill

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