Intermittent compressor no-start trouble-shooting

[idickers]

I need some help with a compressor that is increasingly tripping the circuit breaker on startup. The compressor is a 15 year-old Campbell Hausfeld (7 hp, 60 gallon tank, single stage, 13.5 scfm @ 90 psi) that is run off 220V wired to a 40 amp (edit: it is 20amp) double pole breaker. Over the past couple of years I have occasionally run out of air, only to discover that the compressor has tripped the breaker. Recently this has been happening more often, to the point this weekend that I can't get any work done with a grinder or cut-off wheel because the compressor trips the breaker.

From reading through the forums, it sounds like I should be looking at check valve out of the tank, the start capacitors, or the pressure switch. The pressure relief valve works when the tank fills up, and there is no leaking where the line from the pressure relief valve connects to the pressure switch. I don't have much experience with the workings of compressors (although I think I'm about to), and have a couple of questions:

My multimeter (Fluke model 73) does not have a capacitance setting, is there a way to check capacitors at home or should I have a shop check them?

How does the check valve fail, and how does this stop the compressor from starting?

How can I trouble-shoot the pressure switch?

Thanks in advance for any guidance!

 

[Citation]

I think there are a few other things to check but to answer your first questions..

No easy way to check capacitance with a Fluke 73. You could buy a second meter that could check capacitance for $20-30.

It could be a issue with being cold. My Emglo hand carry compressor doesn't like starting in the winter in my garage. That is partially because of my next point, check your wiring. My father is not wired correctly at the house and I get some serious voltage drop when the compressor starts. That drop reduces motor torque which results is a stall and the motor's internal breaker pops. For me this is a problem on cold start. If I've been using the compressor and it's warmed up then this isn't an issue. Check the line voltage during start. It's possible you have a wiring issue that's causing a voltage drop.

BTW, in your case is it the motor's breaker or the panel breaker that trips?

Ok, the underloader and check value could cause the same issue. At start the motor can't push the piston into a pressurized cylinder. The unloader is that thing that hissed at the end of a cycle. The check valve ensure the tank pressure doesn't make it back to the pump once it's off. A failure of either could cause a stalling issue.

Of course the caps could also do it.

 

[LS6 Tommy]

Start switch could be going,too. Does it trip the breaker instantly, or try to start, run slow and then trip?

Tommy

 

[haptiq]

The pressure relief valve will let you know its working by making a hissing noise for 10 seconds after the motor shuts down. It is bleeding the residual pressure out of the pump cylinder(s) so the motor has a chance to gain momentum on the next startup rather than start the pump under pressure. I just replaced a capacitor that tested bad on my 5 hp compressor. The guy at the motor supply place told me that capacitors are either good or bad, no in between FWIW. Look for bad cap connections ie. signs of heat. If you aren’t scared of electrocution, check voltage at the input to the motor while starting or running to verify circuit integrity. Of course check your pump oil too.


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[idickers]

Thanks for the suggestions. When it trips, it is the panel breaker in the basement, and it happens instantly. There is no running at all, just a faint click that I can hear echo in the tank. When I go down into the basement and flip the breaker it starts right back up. I'm confidant that the wiring is fine, but I can check the voltage easily enough.

Good point about the cold, but in the past it has reliably started when the temp was below zero and its in the 40's right now, and this problem has been occurring over the summer as well.

 

[Dentaltec]

https://fix-my-compressor.com/compressor-trips-the-breaker-on-restart/

if it was running and running Id say its time for a mag starter, since its tripping the breaker this will help you

 

[dreamingmuscle]

Breaker might be getting week also. Dentaltec posted a great trouble shooting guide though

 

[The Cobbler]

The pressure relief valve will let you know its working by making a hissing noise for 10 seconds after the motor shuts down. It is bleeding the residual pressure out of the pump cylinder(s) so the motor has a chance to gain momentum on the next startup rather than start the pump under pressure. I just replaced a capacitor that tested bad on my 5 hp compressor. The guy at the motor supply place told me that capacitors are either good or bad, no in between FWIW. Look for bad cap connections ie. signs of heat. If you aren’t scared of electrocution, check voltage at the input to the motor while starting or running to verify circuit integrity. Of course check your pump oil too.


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you mean the unloader valve. pressure relief is there to blow off in an over-pressure situation

 

[matt_i]

if it was running and running Id say its time for a mag starter, since its tripping the breaker this will help you

In my mind a coil operated device could help, but that would be due to the pressure-switch having a high resistance (= damaged) contact or contacts from directly starting the motor.

So along those lines it might be better to inspect the pressure switch first (many times contacts are open and visible under the cover) If you see arcing or carbon tracking, and a new one solves the problem, then the path of a heavier duty coil-operated contact set would be a nice long-term improvement.

 

[idickers]

https://fix-my-compressor.com/compressor-trips-the-breaker-on-restart/

if it was running and running Id say its time for a mag starter, since its tripping the breaker this will help you

I'm not familiar with a magnetic starter, how would that be used in this application?

 

[idickers]

Breaker might be getting week also. Dentaltec posted a great trouble shooting guide though

Do you have a link for that breaker trouble-shooting? I must not have my search mojo working, because I could not find it.

 

[idickers]

I think the check-valve is okay, as I can disconnect the line to the pump head or the unloader valve and don't detect any hissing or leak.

 

[OccupantRJ]

Loose belts can also jolt a motor on startup and trip the breaker.

 

[idickers]

Loose belts can also jolt a motor on startup and trip the breaker.

Thanks for the thought. Belt seems good: firm tension, no cracks or glazing.

 

[ob355]

As stated above, check the breaker. Breakers are thermal protection if its happening at start up it would take a lot of power to heat up the breaker that fast (like a bad motor or wiring). They have arc fault breakers that will trip if an arc is detected, i had problems with some power tools with those. If it happens after replacement it will narrow down you search.

 

[idickers]

The capacitors test good, and I hear the unloader valve go off after filling the tank, so it appears to me that the likely culprit could be the start switch, the circuit breaker in the panel, or the motor. I suppose I could test the motor by disconnecting the belt and seeing if the problem goes away.

 

[KenC]

I'd swap breaker in the panel first, much easier. Removing the belt really doesn't help isolate because you've removed the breaker load as well as pump load.

 

[Todd.Brock]

Is the “start switch” the pressure switch? When the pressure switch cuts in , it has to connect and disconnect the power. That is hard on a pressure switch. I am surprised it even has a pressure switch rated for 40 amps. A magnetic starter is similar to a relay that does the power switching when the pressure switch calls for air. It completes a circuit to tell the mag switch to power on and run then motor. When pressure requirements are satisfied, the pressure switch interrupts the circuit and the mag switch disconnects the power.

 

[LS6 Tommy]

Th start switch is a centrifugal switch inside the end bell of the motor that removes the start winding from the circuit at approximately 40%-60% of full speed. If it isn't opening, the breaker will trip.

Tommy

 

[Warrenator]

Another vote for the centrifugal switch. You can open up the motor and see a brass assembly with springs on the end... that needs a bit of cleaning and oiling occasionally. If it has gotten stiff if won't move easily and the breaker trips.

 

[Markfothebeast]

I had two compressors trip breakers. Both were due to failed capacitors. One was a Campbell-Hausfeld and the other was a Walmart special as well.

I also had one with a leaking check valve that'd trip the breaker ONLY with air pressure in the tank fighting the startup of the motor - causing excessive amperage draw. With no air in the tank, it'd start fine.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[idickers]

I am surprised it even has a pressure switch rated for 40 amps.

Oops, I'm a ****. It's a 20 amp 2-pole breaker.

 

[Bert_]

If this compressor is anywhere near a real 7hp, then a 20a breaker is grossly undersized. A real 7hp motor would pull ~30A under load, and require a 50-60a breaker though you could go larger yet.
Is this actually 7hp or is it 7hp "peak" ?

 

[7635tools]

If this compressor is anywhere near a real 7hp, then a 20a breaker is grossly undersized. A real 7hp motor would pull ~30A under load, and require a 50-60a breaker though you could go larger yet.
Is this actually 7hp or is it 7hp "peak" ?

Second that. I have a 7 1/2 horse compressor and the FLA on the motor is 28 Amps. It should be on a minimum 40 amp breaker.


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[idickers]

Is this the centrifugal switch? This is from the side opposite of the pulley, on the side were the capacitor wiring enters the housing. If I understand how the switch works, the two "ears" riding on the tabs and held by the springs should move outwards. I can move them with a screwdriver, and they seem to stick in the outer or inner position. I can't really see the "points" that I've heard described.

I'm also not sure how I would service or replace this switch. The out bearing does not have any obvious set screws, and may be interference fit. So I guess I'd have to heat the bearing with a torch to get it to expand for removal, and then replace it when reassembling.

 

[idickers]

If this compressor is anywhere near a real 7hp, then a 20a breaker is grossly undersized. A real 7hp motor would pull ~30A under load, and require a 50-60a breaker though you could go larger yet.
Is this actually 7hp or is it 7hp "peak" ?

Good point. They may be taking artistic license with the phrase "horsepower". The sticker on the motor says 17.3 amps. It's an old A.O. Smith motor which isn't made anymore, but the current most-similar replacement is listed as 5 hp.

 

[Milton Shaw]

The switch is mounted to the end plate you removed. That part on the shaft that moves just moves those fingers of the switch. The switch has at least two wires to it and you can see the points easily. That part on the shaft if it moves is usually ok.

 

[Bert_]

Good point. They may be taking artistic license with the phrase "horsepower". The sticker on the motor says 17.3 amps. It's an old A.O. Smith motor which isn't made anymore, but the current most-similar replacement is listed as 5 hp.

At 17.3A that makes it about a 3hp in the real world, as opposed to the marketing world...

20A breaker is still to small, but if it worked for years until now then there is probably another issue.

I've had those centrifugal switches stick before, from dried out grease, usually nothing wrong with the contacts.

 

[idickers]

I've had those centrifugal switches stick before, from dried out grease, usually nothing wrong with the contacts.

Where should the switch be greased?

 

[idickers]

At 17.3A that makes it about a 3hp in the real world, as opposed to the marketing world...

20A breaker is still to small, but if it worked for years until now then there is probably another issue.

It sounds like I may need to upsize my circuit. Perhaps my circuit (20 amp double pole breaker with 12 ga wiring) was right on the edge of reasonable when the compressor was brand new, but after 15 years of use and abuse the electric motor may be less efficient than new. I asked an electrician, and got this response:

"1) The circuit conductor is sized at 125% of the motor FLA rating. Therefore, 18 amps x 1.25 = 22.5 amps. Use 10 AWG copper conductors which are rated for 30 amps.

2) The breaker is sized at 250% of the motor FLA rating. Therefore, 18 amps x 2.5 = 45 amps. Use a 50 amp double pole circuit breaker. Per code, the breaker is sized at 250% higher due to the "in-rush" current upon the motor start-up."

The wire gauge makes sense, but I'm surprised at the 50 amp breaker recommendation.

 

[KenC]

I think you're on the right track now. But, I'd still change the breaker to another in the panel first just to be sure it's not simply a breaker gone bad. If it used to work, it should work again.

 

[idickers]

What do think is the appropriately sized breaker for this application? After reading a bit on how inverse time" circuit breakers actually work, it sounds like 30 amp should be fine for this application.

 

[Markfothebeast]

Now that I took a second look at the initial post, I wasn't thinking about breaker, amperage draw, and wiring size. My 3.7 HP 240v unit runs on a 30-amp circuit with the appropriate 10/2 wiring. This unit is labeled directly on the electric motor with the amperage, as should yours. Using a 20-amp breaker with a 7-horsepower electric motor made me giggle there. This is most likely why it is switching off the breaker. This 7-horsepower may or may not be a falsely advertised number, which is what makes this difficult. Find the PDF manual and read up on breaker size for this particular compressor.

There are running amps and full load amps. Lets use 15 running amps as an example. When the motor initially starts without air in the tank, there's less resistance to work against. With air in the tank, the startup process requires much more energy. With the motor started and running, (example) roughly 15 amps is being drawn. Multiply this number times two for a rough estimate of load startup amps to get 30 amps. This is my exact setup and I run a 30 amp breaker. My compressor is also advertised at nearly half the HP rating as yours at 240v. Having adequate current available to the motor will also extend it's life expectancy

Determine your motors running or load amps and appropriately size your breaker from there. 20 amps sound far too little to startup a "true" 7HP motor under load. I say "true" due to falsely advertised HP numbers. At the very minimum I'd be running 50-amps with 6-gauge wiring, preferably 60-amps with proper wire gauge size. I did not read what the amp draw is on your compressor so this is going from the 7-HP number.

20 amps is rated for 12/2 electrical wiring which is fairly standard for home outlets. If you're running 12/2 (or a 12/2 power cord), you'll need to run thicker gauge wiring to comply with current demand. It's not advised to simply "plug'n'play" breaker sizes like computer components. Think of breaker amperage and wire gauge sizes as a package deal. They are intended to match up with one another (National Electrical Code) for safety reasons. Wire size chart below.



-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Markfothebeast]

I looked around a bit at 7.5HP 240v motors (didn't see any 7HP units). Most of what I saw are rated anywhere from 20 to 39 amps FLA (Full Load Amps). So I overestimated a bit. If your compressor is rated around 30 or so full load amps, you'll be alright with a 40-amp breaker. 50 amp would be okay as well. But you'd definitely want to use 8-gauge wiring with 40 amps or 6 gauge with 50 amps. I ran a bit bigger wiring and breaker than I needed for future upgrade purposes.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[idickers]

Thanks for all the information! I checked on the motor, and its 17.8 amps, so probably closer to a real 3 hp. From the discussion it sounds like I should pull some larger wire, probably 10ga, and use a 30 amp breaker. Does that sound about right?

 

[Markfothebeast]

Thanks for all the information! I checked on the motor, and its 17.8 amps, so probably closer to a real 3 hp. From the discussion it sounds like I should pull some larger wire, probably 10ga, and use a 30 amp breaker. Does that sound about right?

30 or 40 amps will be okay. If you someday plan to upgrade, go 40 amp/8ga. The breakers should be the same price. But the wiring isn't! Wiring prices have gone through the roof..

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Bert_]

Where should the switch be greased?

IF the switch is sticking, clean off all old grease and put a SMALL dab where the parts slide.

 

[idickers]

Thanks for all the help. Two weeks ago I pulled #10 wire and put in a 30 amp breaker, and all is well. I've used a lot of air grinding/cutting since then and had no problems with compressor restarts, so it must have been the marginal wiring.

 

[6PTsocket]

Th start switch is a centrifugal switch inside the end bell of the motor that removes the start winding from the circuit at approximately 40%-60% of full speed. If it isn't opening, the breaker will trip.

Tommy

If you can run the motor briefly, when it shuts off and is slowing down you will hear a distict click when the centrifugal switch closes to prepare the motor for the next start. This is nor a complete check of the switch but it will at least tell you if it is opening. If the contacts are shot you might get that situation where sometimes it starts and sometimes it dosen't. That is what connects and disconnects the capacitor.

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