You’ve got a full tank of air. The air tool ramps up nicely and is working well. Then, and as the pressure in the tank drops to the cut in pressure setting, rather than the compressor starting to rebuild the air in the tank, when it tries, the compressor trips the breaker on restart. If it’s a fuse in the circuit instead of a breaker, when attempting to restart, the compressor blows the fuse. The information on this page includes:
-what’s happening when the compressor trips the breaker or burns the fuse on restart?
-what needs to be checked on the air compressor when that happens?
-what are the compressor components involved and how to check them?
What’s happening when a compressor trips the breaker / fuse on restart?
When the air compressor tank is drained down to the cut in pressure level, the pressure switch reacts to the drop in tank pressure, it trips to “passing” (as in, the current now flows to the compressor motor) and the compressor should start and run until the compressor tank pressure has reached the normal cut out pressure setting, at which time the compressor should stop and wait for the tank air pressure to drop to the cut in pressure level again.
At the cut in pressure setting the the current will flow first through the pressure switch and then through the motor start circuit, and for a huge number of different makes and models of air compressor, the current then flows to a start capacitor.
If a particular compressor motor does not have a start capacitor, often that’s a small, sub-fractional motor, and there is sufficient current in the electricity flow to kick that motor into turning.
Larger compressor motors require a “kick start” to get going, as there is not enough power in the circuit to to feed what the compressor motor needs on start up, and that’s called the “inrush current”.
If for some reason the motor cannot start, it will continue to draw power, and may pull enough amperage to exceed the capacity of breaker or fuse and as a result the compressor trips the breaker or fuse on restart.
What are the things on the compressor to check when the air compressor trips the breaker or fuse on restart?
Did the unloader valve work? Sometimes the unloader valve fails, and as a result, some compressed air is trapped over the cylinder piston. That trapped air adds to the load the compressor motor experiences on start up, and that additional load may be enough to force the motor into pulling too many amps and popping the breaker, or blowing the fuse.
To test for this, unplug the compressor, open the tank drain and drain all the air out of the compressor tank (which you should do after every use of your air compressor as part of the regular preventive maintenance), plug the compressor back in and if your compressor has one, flip the ON/OFF switch to on.
If the compressor starts this time and the breaker doesn’t pop, that suggests that your air compressor unloader valve is not working properly, one of which made by Square-D is shown in the image above, and you need to either fix it or replace it. To be sure, shut off the compressor, drain the tank again, and try to restart it with an empty tank. If the compressor starts easily again, then it’s pretty much certain that it’s the air compressor unloader valve failure that is causing your air compressor to trip the breaker on restart.
Are you plugging the air compressor into a power bar or extension cord? Home use extension cords are notorious for throttling power, as is a power bar. You may be under powering your compressor motor, and the resulting overheated motor may be contributing to the breaker tripping when the compressor starts.
Leave the compressor to cool for 15 minutes or so, and then try plugging the air compressor power cord directly into a wall socket, preferably one that has a 20 amp breaker, and has no other electrical devices using power at the same time as the air compressor is trying to start.
If the compressor starts this time, and after you have used some air and the compressor successfully restarts when the tank pressure drops to the cut in pressure setting, then you’ve nailed down the problem.
As a general rule we suggest that you add air hose to get the compressed air to your work station as opposed to using an extension cord to move the compressor closer to where you want to use compressed air. Nothing gets damaged if it doesn’t get enough air through a long hose. On the other hand, electrical devices are overworked if their power supply isn’t up to what is required leading to electrical maintenance issues.
Is it the pressure switch itself that has failed? Less likely, but still possible, that your air compressor trips the breaker on restart can be cause by a pressure switch that has shorted out.
When the air pressure in the tank drops, a diaphragm inside the pressure switch moves, and ultimately, that moving diaphragm forces the points inside the pressure switch to touch, a circuit is made, and power flows to the compressor motor starting it, and driving the pump to pump more air into the compressor tank.
Turn off or unplug the compressor.
Drain the compressor tank and then close the drain.
With due regard to the presence of live terminals inside the pressure switch, pull the cover off, reset the breaker, and watch inside the pressure switch to see if there is any arcing or sparking when you turn the compressor back on.
Since the pressure switch points should already be touching with the absence of air in the tank, there should not be any arcs or sparks, and if there are, that’s a pretty good indication that you pressure switch may be the problem.
You will need to replace the pressure switch.
Has the compressor capacitor failed?
If the compressor has a start capacitor, or a start / run capacitor, or two capacitors, the failing of one may mean that the compressor will blow a fuse or circuit breaker when attempting to start.
This is what a typical motor capacitor will look like:
The correction of the problem of when the air compressor trips the breaker on restart becomes increasing complex once these earlier tests have been made. One of the more complex tests is that of testing the capacitors.
If useful for you, please follow this link to our page that describe what the capacitors are and about how to test them.
Compressor motor windings shorting? In our opinion the next component that will be suspect when the compressor trips the breaker on restart are the motor windings shorting, or any of the electrical connections inside the motor that may be shorting and the sudden flow of electricity to ground pulls too many amps.
If you have reached this state in your compressor problem diagnosis, and you are not skilled in electrical motors or electrical circuitry, we suggest that you get your compressor motor to an electrical motor shop for a load test to try and determine what, if any, part of the motor is shorting.
These are a few of the typical reasons why an air compressor trips the breaker on restart. If you have experience with other scenarios, why not share them with visitors using the comment box below? If you see a comment and you would like to add to it, please feel free.
It is always helpful if you identify the make and model of your air compressor in any post.
Hi, I have an old Husky Air Scout 1.5 gal 135 psi max air compressor that I bought from a friend for cheap. I have used the compressor maybe 25 – 30 times at 100 psi with no problem. I plug the compressor into a wall outlet connected to a 20 amp circuit breaker. last week when I tried to use it, it worked fine for the first 15 inch mower wheel. I shut it off after bleeding the air. (there is a bleeder valve on the front) . When I tried to turn it on again an hour later, It blew the fuse that was in a fuse case on the front. I went to the hardware store and bought a 4 pack of fuses. It blew all four (one at a time) as soon as I turned the compressor on. It never got a chance to compress any air. Put new fuse in. Turn on compressor. Blown fuse immediately. There is no circuit board that I can see. There is a pressure switch (120vac 10 A) in the unit. Can anyone tell me what might be happening?
Hi, is there someone that can help me
It is model 919.176841 Craftsman 4hp 20 gallon horizontal air compressor.
The problem is it will start and go up to proper tank pressure with no problem.
But then if you use the air hose and the pressure drops to around 75, which is
normal, it goes to start again, and it barely turns. If I leave it trying, it will kick
out the reset on the motor. If I disconnect the big line that comes out of the
compressor head, it starts fine. I took off the air filter, and it wasn’t that.
I replaced the unloader valve at the switch on the smaller air line. Nothing
changed. But, if I push down the little reed valves while it trys to restart,
it restarts fine. I just hold down the reed valves with a small screwdriver
just long enough for the compressor to get up to normal rpms. Then it runs fine.
It will run all day long once it’s started. I used a blow gun attachment to
keep bleeding off air pressure while it was running, and it keeps runnning
fine and building pressure with no problems.
? I’m stumped here. Please help
I am facing the same problem 100 hp fini air compressor tripping the breaker . Checked the motor winding no shortage how can i check step by step found the exact problem
Hello, this website is really helpful! I have an Eagle Silent Series .75-HP 1-Gallon Hot Dog Air Compressor, and am having issues with the breaker tripping while the compressor is running. It happens very sporadically. Sometimes it occurs every few minutes, sometimes every few hours. I have replaced the capacitor on the compressor. From this page, it sounds like it may be an issue with the compressor being underpowered. Besides plugging in directly to an outlet, do you have any suggestions for remedying this issue?
It’s difficult to be certain what the issue may be, Tianna. For example, when the compressors is running, does it run for long periods at a time… hours instead of minutes? If so, could be that the motor is overheating due to it not having time to cool between uses. This relates back to the Duty Cycle, and if you commonly exceed that with a compressor, that’s how the motor reacts. This compressor has a 50% duty cycle, meaning that for every period of time – in 10 minute increments, not hours – the compressor must sit unrunning for an equivalent period of time for it to cool. Could this be the issue?
And if the compressor trips the breaker after it’s going/ pumping out air? Anything on the compressor that would caused that or is it just an overloaded circuit now?
Thank you for your help.
Sorry, not clear. Are you saying that the breaker trips after the compressor has started, and is pumping air into the tank? If so, what pressure does it pop the breaker, please. And, what’s the make and model of yours? Thanks.
I have the Hitachi ED-12 compressor. I was having trouble with the compressor starting and getting up to speed. It would eventually blow a fuse.
I did what was suggested and opened the drain valves and it has no problem getting up to speed right away. I assume that means the capacitors are fine and from what I have read, you need to replace the “unloader valve”? I am not sure where that is in my unit?
Could you be referring to the non-return valve? Item #53 in the pic below? I see on a parts site it says to replace that if you are having these issues.
I got this unit for free and it has been great, I don’t use it that often, but like to have it for winterizing my pool shed and sprinkler system.
I appreciate all your feedback
Hi Chris. I’ve modified your post somewhat to remove many of the off-site links that didn’t really help.
First, you are referring to the EC12 compressor, yes?
You say “I did what was suggested and opened the drain valves and it has no problem getting up to speed right away. I assume that means the capacitors are fine and from what I have read, you need to replace the “unloader valve”? I am not sure where that is in my unit?”. Opening the drain valve removed over-piston air load, and emulates the function of the unloader valve. If opening the tank drain valve worked, the first check is the unloader valve. After the compressor gets going, close the tank drain, and let the air pressure build up to cut out. As the compressor stops on full pressure cut out, liste around the pressure switch (yours appears to have an internal unloader valve) to ensure that there is an quick burst of air from the pressure switch signifying that the compressor has unloaded.
If the compressor unloads, then it’s quite likely that the issue IS the start capacitor being weak.
You say “Could you be referring to the non-return valve? Item #53 in the pic below? I see on a parts site it says to replace that if you are having these issues.”, no, I am not. I am referring to the unloader valve that is part of the pressure switch.
Right, It does hit full pressure and will stop. I dont recall hearing a his release but will check again. Also, is there a “foot valve” that will keep the pressure in the cylinder head as well that might need to be replaced?
Also, can the unloader valve be serviced/cleaned and it looks like on my unit, I have to replace the whole apparatice that houses the valve? is that correct?
Remove the cover (carefully) of the pressure switch, empty the tank, start the compressor, close the tank drain, and monitor the unloader which is a part of the pressure switch on this compressor. If it works, check the start capacitor. See how here: http://fix-my-compressor.com/is-the-compressor-start-capacitor-working/
The “foot valve” you refer to is the tank check valve, and it’s in the fitting where the air line from the pump head reaches the tank. If air pressure stays in the tank after the compressor has stopped and unloaded, it is likely working fine.
i started it up again with an empty taNK. starts no problem and runs but dont shut down it gets to a point that it is working hard then stops and hums, full tank of air. so some pressure regulator switch is the issue for sure.
No, I don’t think so. Check the capacitor, Chris.
Fair enough, but how do I find a discontinued part? Can i just get a same or similar spec capacitor?
The photo shows a 40 micro-farad capacitor, and the voltage. It doesn’t show the spade or connector types on top. As long as you get a new cap with the same ratings, and it fits your compressor, it should work fine.
Okay, I pulled the caps. they seem fine. I was only able to test continuity and they seemed to be fine for continuity.
Here are some pictures. I don’t have a capacitor tester
how do i find a replacement cap. without going to original OEM spec cap?
What size am I looking for? Granger.ca seems to have them in Canada/.
Hi Chris. Does this page not provide enough info: http://fix-my-compressor.com/finding-a-new-compressor-capacitor/
If not, add a comment. Thanks.
Hi there! Great website and very informative!
Ok I bought a used 20 Gallon Porter Cable C5510 air compressor for cheap. The guy said it runs but trips his breaker every once in awhile. I figure he probably had a weak breaker and I should be good. Got it super cheap so didn’t mind taking the gamble.
Ok. My setup is:
– 15A outlet in garage with nothing else connected to it.
When i first install it it was working fine. It would pump up from empty to cut off and then turn on at cut in. Rarely it would trip my breaker.
Fast forward a few weeks, now it constantly trips the breaker.
This is what I’ve done so far:
– replaced pressure switch with Condor MDR11 (built in unloaded valve; which does hiss/release pressure, when I turn the switch off)
– removed, inspected and tested pressure relief valve
– tested the capacitors with a high quality Fluke meter. Both capacitors tested good via capacitance and resistance test.
– I clamped the line cable and with the drain valve open I constantly get around 7.5-8 amp draw. When I close the drain valve to add load to the motor, it starts to climb to around 9 amps. I am not able to test further as it will not pump any higher than 30 PSI.
– with both the drain valve open and closed, the breaker trips. So doesn’t matter if there is a load or not.
– additionally I isolated the AC motor with the pump motor by removing the belt and ran it for 10 minutes and it did not trip the breaker at all. I was getting 5.0 – 5.1 amps constant with this setup. So with that said I really don’t think it’s the AC motor at all. It only trips when I have the pump motor connected.
Furthermore, I did try another outlet and secretly (haha) my neighbour outlet and it still trips the breakers.
Any help would be greatly appreciated. Thank you!
Can you find an outlet wired to a 20 amp breaker and try that? Or, use your meter to check the inrush current draw. I suspect that your power supply is marginal for an older, tired compressor.
Thanks for your prompt response. Unfortunately I do not have any 20 amp circuits at home. I would have to haul it out.
At start up the inrush or starting amperage draw is around 25-30 amps. it does not trip the breaker at that point. it trips after 15-30 seconds, regardless if the tank is empty or partially filled.
Thanks. OK, you’ve cleared everything on the compressor, and the problem persists. So… by deduction, I’m thinking that it must be the compressor, and that it is heating up and creating a short of some kind. I know it didn’t trip the breaker with no load on the motor, but the load increases as the pressure in the tank increases. That’s what I think, and that’s a very difficult thing to nail down. Good luck.
Well I think I got it figured out. Tried 2 things today.
First I took apart the AC motor and inspected the contacts and they we’re dirty so gave it a good polish with sandpaper. Ran the motor with no load and unbelted and amp draw seemed to drop from around amps to around 4.5 amps. Not sure if it made a difference for efficiency or if it’s due to ambient temperatures and conditions vs yesterday. I put everything back together and……… No good! Still tripping the breaker.
So then I then proceeded to the pump motor and took of the cylinder head off and low and behold!!! One of the valve plate reeds is broken!
Hopefully I can source one out locally, if not may have to order it online.
I’ll keep you posted once I replace the reeds…
I just bought a new Harbor Freight McGraw 20 gallon compressor. On a full tank, this morning, while blowing some sawdust, it tried a few times to start, hesitating, then tripped the breaker. My last unit was Central Machinery and it did this from the beginning throughout it’s ONE YEAR life before it failed and I threw it away. All the advice for this problem is always related to older machines with failing parts, never on brand new machines that do this. I don’t want to go through this again. So according to the troubleshooting, I should be looking for a bad check valve on this brand new machine?
Perhaps, but first I’d consider the power supply. Is the supply to the socket where the compressor is plugged in on a 15 amp or 20 amp breaker. Electric motors need higher amperage on start up due to their need of “inrush current” and a 15 amp supply is often marginal once the compressor gets going, but often isn’t enough to deal with the inrush demand of the motor.
willyr, it’s happened again. This time, I used a lot of air blowing and it never kicked on. Almost emptied the tank. Next day,, I was rolling it out to take it back to HF and passed another plug and tried it and it kicked on. So I put it back on the original plug and it also started, but hesitated a lot. My dad says it may be because I have the tool side set to high, at 120 psi. I have since lowered it to 90 psi and am waiting for the inevitable fail, unless that could possibly be why it won’t start or hesitates to start. It hasn’t been tripping the breaker though.
It is the only circuit in my shop that’s not on a 20 amp breaker. Tomorrow I will swap this 15A breaker out with the 20A that runs the lights. That makes more sense. This circuit is for the compressor and any power tools I use, so it needs a beefier breaker, the lights will do fine on a 15A.
You can put it in a 20amp breaker if you have 12-3 wire in the circuit. 14-3 wire will heat up using a 20 amp breaker.
Those were existing breakers, I’ve rewired the shop for 20A since I moved in. Didn’t have a need to change them til now.
I have a Dewalt 4-gallon electric dolly style compressor that works well most of the time. Sometimes though upon start-up the motor starts to run slowly and then trips the breaker. I flip the breaker and try starting again. The motor again starts slow and then will either crank up properly or else trip the breaker again. It does this when fully empty and usually just when it hasn’t been used in a long time.
So, it shouldn’t be the unloader valve and I’m plugged directly into the outlet (no extension cords or power-bars). This happens on different outlets on different circuits so not an electrical source issue.
As my issue is intermittent , where do I start to diagnose?
Dave, have a read of this page, I think it may explain what’s happening on your compressor.
hi sir i have an Italian air compressor mod: (CPRC 3200 NS11S MS) and i use it with a Generator but now it wont run!! when i turn it on its run less than one second and the Generator shutdown!!? but its not the generetor coz when i use the generetor for some things ells its work properly!! so thats mean the problem is in the air compressor!! dont know is it circuit breaker or pressure switch!! or some things ell!?
Sanborn 20 gal that runs for around 30 seconds to 2 minutes. Overheats, and will trip the breaker, unless it’s already run for a couple cycles. Then it trips its own overheat safety and needs to be reset. Does not exceed 110 psi unless connected to a 30amp breaker.
Hi Scott. Per the tips on the page, what have you checked so far please?
have Makita MAC5200, with 0 air pressure the compressor will run up to approx 40psi then blow the current overload switch on the compressor. Reset the switch and drain off the pressure and it runs until it gets to around 40psi then blows the current overload again.
Sure Franz. What did you find when you did the checks? If you’re not sure, navigate to here and scroll down to the appropriate page; http://fix-my-compressor.com/air-compressor-problems-and-fixes/ .
I have checked both the run and the start capacitors. The run capacitor 50 uf measures 55 uf and the start capacitor 300 uf measures 343uf. Would either of those readings cause the compressor problem described above.
I have replaced the pressure switch and that did not solve the problem.
If I run the compressor with the drain valve open it will run without stopping. But when I close the valve it builds up pressure and blows the overload switch on the compressor. It will start again but only for a short time before it blows the overload switch.
I am leaning toward buying the run capacitor but not sure that is the problem and they are not cheap.
Hey Franz. The symptoms you are experiencing on your Makita MAC5200 are symptoms developing from an inability of the motor to overcome an issue.
While I am not an electrician, I believe that since the uf readings on your caps exceed the rated output, that suggests that they are fine.
If they are OK, and the tank check valve is not preventing increasing pressure to enter the tank, the results of which would be an overload situation on the motor and it going off on thermal overload, then I would wonder about the pump itself. For example, is the pressure side of the valve plate working properly? If it is not, it may be the issue preventing air entering the tank and back loading the motor causing the overheat.
I’d pull the pump head and have a look at the valves before buying another cap.
My name is Dave. I have this same exact problem with my MAC5200, but I haven’t started to diagnose it yet other than plugging it straight into a 20 amp socket. What would be advisable?
Hi Dave… when you reviewed the other items referred to on the page, what did you find / see / hear?
Craftsman model 919.167312 6HP 30 Gallon. Starts with no load fills to 140 PSI fine. When pressure drops and it tries to restart it trips the breaker. Unloader appears to be working (I can hear it when I shut it off). If I disconnect the unloader tube, the compressor starts just fine. No air leaks out when unloader tube disconnected- full tank with the machine off so I am pretty sure the tank check valve is OK.
Once I hook the unloader tube back up it trips the breaker. if the tank is above 40 PSI and I try to restart.
Please the see troubleshooting page and scroll down to the start / run capacitor pages. If this were mine, I’d be checking the start cap if all else is OK in terms of power supply. Please check and let us know.
05?. Campbell and hausfield 15 gal. Model # starts with hl4. Fills tank to 125psi and shuts down. On restart hums.and trips breaker if sont unplug immediately. Replaced pressure switch unloaded valve check valve and start capacitor. Not on extension cord. No sparking. Does same thing. Please help
Carol, the humming is from the motor. It’s trying to start and cannot and cannot do so against load. That the compressor will start with no load (no air in the tank) and fills to 125 PSI and shuts of normally, suggests that there is no pump i8ssue.
Then, when it tries to restart with air in the tank it cannot. If the start capacitor has been replaced and is working properly, then that points to the motor itself as being the problem.
For example, some compressor motors have a centrifugal switch that will allow the motor to start with no load, and then, as back-pressure from the filling tank increases the motor load, the switch trips to allow the motor to handle that. That’s just one scenario.
I think you need to have the motor checked out.
Just replaced pressure switch. Didn’t work. It does hum when trying to restart but tank full, not empty. I am using extensions cords as built a new shed and need for siding. Will try to figure out what start cap is but the pressure switch was a major job. Took me almost 2 hours. Any suggestions most appreciated.
Campbell.and hausfield compressor
Carol, same answer… “If it’s humming on the restart, it’s also time to check the start capacitor. Does it hum on start with the tank empty. If so, that doubly suggests the start cap is failing. See the page under general troubleshooting on how to test that, if you aren’t sure.”
However, if you are using an extension cord that’s too small for the motor power needed, that, too, will cause a humming motor.
Move the compressor to a plug where you can plug it in without an extension cord. If it works OK, your extension cord is too small a gauge.
Found the capacitor on Amazon. Delivered today and installed but can’t test till 3.(daughter works nights). My concern is it looks dirty.and scratched up.. Cross your fingers.
What looks “dirty and scratched?, the new cap? That being the case, send it back, unless you bought a used one.
Update. Didnt work. Still hums and won’t restart. Get 1 tank of air then trips if I don’t unplug right away. Help. Running out of things to replace. Need for job asap. Should I give up and buy another one.
Hauled it back to garage, not the extension cord. It is a heavy duty. So i filled, let some out and when it tried to restart hummed and was unable to. Pull power, drained and same.thing. From reading your troubleshooting several times (this all above my pay grade), I assume you think it’s the start capacitor. Which I can not seem to find but in the interest.of dumping more money andntume in this wanted to confirm. Thanks so much for your help
You are welcome. Check this page for more information on the motor start capacitor: http://fix-my-compressor.com/is-the-compressor-start-capacitor-working/
Campbell and hausfield compressor from mid 2000 so it’s old. Runs till pressure up, leaks out of uploader valve. Tries to restart but can’t. Replaces uploaded valve. No change. Will tries to restart hums. Strange thing is after unplugging, still makes a noise like shorting for a few seconds. Any help appreciated
Carol, if air is leaking out of the unloader valve when the compressor is stopped, you’ll likely need to clean / replace the tank check valve.
If it’s humming on the restart, it’s also time to check the start capacitor. Does it hum on start with the tank empty. If so, that doubly suggests the start cap is failing. See the page under general troubleshooting on how to test that, if you aren’t sure.
Before you go thinking it’s any of these… I checked on the back of the cover that holds the capacitors and found a lever activated thing that’s plastic and pushes on a thin piece of metal… It rests upon the motor shaft… here the cover was broken causing it to not rest against the shaft and it didnt push the plastic lever against the metal to make electrical connection that goes to your start up capacitor… I glued my cover back together at the mounting screw where it was broken, mounted it and that solved my problem… good luck!
Air compressor issue. 6.0 hp 60 gal tank. Condor Md 11. My compressor will not restart when after being filled it hits the cut in pressure. I replaced the pressure switch and unloader valve. The unloader valve works great when fill pressure has been reached but when compressor hits cut in pressure it labours to start and trips the breaker. I disconnected the unloader valve line and put a manual ball valve on the end of it. If i open the valve when the cut in pressure is reached the compressor will start fine, I close the ball valve and compressor reaches capacity. I open the ball valve again and air purges out and stops. no bleed. Close the valve and open it again when cut in pressure is reached and compressor starts fine, repeat. Could the check valve be the problem, there is no air bleeding from the unloader valve when the tank is full.
You’ve checked and the unloader actually unloads when the compressor reaches cut out! So if there is no pressure over the piston, why isn’t the compressor starting with a load in the tank? It’s time to check the motor capacitor to find out. See this link for more info.
Thanks willyr, There is no air above the cylinders as I tested by manually purging it before start up. I figured if the capacitor is failing or bad will it just quit all together and not allow the motor to start. Could it just be weak and not giving the full power the motor requires?
Quite likely. You’ll need to test it/them to be sure.
I have an old sears paint compressor model 106.15451, where would I find the unloader valve? It’s tripping the breaker after the pressure falls to refill again. It starts up perfectly when no air in the tank.
Hi Elvis. I can’t see the pressure switch on this compressor, as I have no photo to check. So, is the present unloader on the pressures switch? If so, likely the fasted way to correct this issue is to replace the pressure switch with one that has the same type of unloader. If you’d like to add a photo of your present pressure switch from both sides and bottom, we’ll try to help further. You can add photos as a reply to this thread.
willyr 0 air in tank cold sttart
OK, no air in tank, starts compressor, runs 10 seconds and trips 20 amp breaker, one new capacitor, right? Is there another cap and have you tested it? It’s a 220 Volt motor I presume? Without the belt on, can you turn the pump sheave relatively easily?
120 volt, no belts and yes when i take cover off can spin motor and crankshaft freely. Oh ya has two capacitors one new the other is good so I’m told.
Update July 14/19 – sticker on cover says 5hp 20gal 12o volt plugged into outlet no ext cord it’s a pro air 2 if that helps
Don, did you not write earlier that it was a 5 HP compressor? Seems odd that a 5 HP has a 120 Volt motor? No way 120 V can run a 5HP motor properly. And it is a Devilbiss right, since that’s the page on which you posted originally? Do you have the model number?
Are you plugging it right into the socket or using an extension cord, please? And also, please keep the thread on one page if you would.
Don, I see that you’ve added that it’s a ProAir 2. When I go looking for that model I find that it is Devilbiss that has the ProAir line, but cannot find a ProAir2 on a 20 gallon tank. The specs I’ve seen say that it’s a dual voltage motor, meaning the motor can be powered by 120 or 240 depending on how the motor is wired.
Assuming the condition is a new one, and assuming that you are not using an extension cord or power bar to plug in the compressor, and now knowing that the pump moves freely, my money is on one of the capacitors still not working, or the motor itself.
This page will provide information on how to test the capacitors: http://fix-my-compressor.com/is-the-compressor-start-capacitor-working/
This page will give more info about that: http://fix-my-compressor.com/finding-a-new-compressor-capacitor/
A bad start capacitor can look the same as a bad unloader valve. To differentiate the two,: 1) get the compressor into the situation causing the non-start (i.e. pressure in tank but dropped enough to cause a an attempt to restart). 2) Turn the compressor off and reset the breaker if needed 3) Unscrew the unloader tube (the small one) from the check valve.
If a little air comes out when you do this then stops, your unloader valve probably wasn’t working. If air continues to come out, then your check valve is not working and needs to be cleaned or replaced. If no air pressure came out when you did this then the unloader valve probably is working properly and already did its job.
In the last case, screw the unloader tube back in and try to turn the compressor back on. If it starts normally then it was probably the unloader valve or check valve. If it labors to start and then blows the circuit again then I would look at the start/run capacitor(s). or possibly, shorted windings
Hi great writeup. I have an issue with my compressor where it will only trip the breaker on my generator but when its used on mains power it works flawlessly. Any ideas on that one before I start working through your recommendations above ?
I suspect that the inrush demand of the motor on the compressor exceeds the output capacity of the generator. I don’t believe, if the compressor works well on the mains, that it’s a compressor issue, but rather, an issue of the generator being under-capacity for the demand.
I have a 20 kw disel gen set. My compressor will start but blows breaker at 50 lbs pressure. The motor for compressor gradually powers down greatly as it reaches 50lbs. Am miffed. Help me??
Per the list of items on this page Ray, can you please advise what you have checked?
I have a a DevilBiss manufactured single piston 12 gallon 1hp CRAFTSMAN model number 919.174212. It’s been working great for years now. I’ve changed the oil frequently with Amsoil synth for compressors. I’ve drained the tank and changed the inlet filter and after use I leave the compressor off. It usually doesn’t get much use occasionally filling tires and once in a while running an impact wrench, but that’s all. Resently it started throwing breakers. This model doesn’t have a pressure release motor start valve so that can’t be the problem. It only throws breakers when the tank is full and the pressure goes slightly down from using a tool… it struggles to turn the compressor and then throws a breaker. I tried using a different breaker line. I just changed the starter cap (the old one tested fine on the multimeter, but thought I’d take a chance) but it did fix the problem. Is it the motor? I mean it runs great when there’s zero pressure and fills up the tank easily. Could it be the pressure switch? What the best way to test for that?
You have a great website! Thanks in advance!
Thanks for your kind words. When an air compressor tank has air in it, there is back pressure against which new compressed air has to work to get into the tank. This adds load to the motor making it work harder to try and start. If you are not using ANY extension cord or power bar, your start cap is good, your unloader vent (you likely have a small hole in the line from the pump to the tank which bleeds air all the time the compressor is running and stops when the compressor stops) is open allowing air over the piston to vent, then I would expect the problem is the motor itself, whether something in the motor has failed (centrifugal switch if one, windings shorting, brushes worn if there are any etc. ).
I have my Dad’s old Champion compressor, a two-cylinder, The sticker on the motor is too faded to read but I am guessing it is 3/4 hp to 1 hp. I have it on a 20 amp breaker and a 5′ 12/3 cord.
It initially starts fine and goes up to 100 lbs when where I have it set to cut out. I can hear pressure being bled off the cylinders by the unloader valve after the compressor shuts off so that seems ok. But, when it is time to restart, the motor runs about 10 seconds and before it really gets up to speed the breaker kicks out.
When the breaker kicks, the compressor pulley seems fairly easy to turn by hand–I don’t know what to expect but doesn’t make sense (to me) that the motor is too weak to turn it.
So I started by replacing the check valve–which was completely shot and definitely needed it. No change. Next I did the pressure switch, which came with a new unloader valve. No change. Then I replaced the start and run capacitors. No change. New belts and they aren’t slipping.
If I bleed off the pressure to about 30 lbs by turning the compressor off and running a tool for awhile, it will start up and fill the tank as it should. Seems like it could the unloader valve is not letting off all the pressure, but what are the chances of both the old and new unloader valve being bad?
Any ideas would be appreciated. I hope it isn’t the motor!
Zeroing in on the capacitors was a good idea, as that would be my first thought based on your compressor symptoms. Your power supply looks good based on your description. Replacing the check valve was a good move. If I understand correctly, the compressor pump starts fine with the tank empty, but will not properly restart if there is air in the tank? Things that may be causing this are a faulty valve in the pump (don’t know where for sure, but maybe from the second cylinder to the tank if it’s a two stage or one of the cylinders if it’s just a twin) or the motor itself has an issue with the power on start up against load.
Thanks for your reply.
Yes, if I start with an empty tank the pressure will build up to 100 psi no sweat. But, when it is time to restart, the motor will run for about ten seconds and trip the breaker.
If I just bleed off air pressure down to 30 pounds it will restart, but if I only bleed it down to 40 pounds when I flip the switch on it will kick off the breaker again.
It isn’t a two-stage, just an ordinary twin. This is an old horizontal tank type on wheels.
But I am afraid I don’t know what you mean by a faulty valve–could you explain how that would work? It does seem like if the check valve is working OK, and the unloader valve is OK there shouldn’t be any extra pressure that the motor is working against. But that motor just doesn’t quite get enough momentum to keep going.
It would be too bad if it is something in the compressor–I doubt there are any parts for this thing–it is pretty old.
I do have an another motor I think might fit that I could throw on there and see what happens. It is a 3/4 hp 3450 rpm, though I think the one that is on there now is a 1140 or 1725–it runs pretty slow.
Any thoughts? Thanks again!
Could be the motor… which is easier for you. Swapping the motor or opening the pump head to have a look at the valves. It’s the valves inside the pump to which I referred earlier, Charles.
HI Willy–my question about the valves would be, what would I look for? Don’t these cylinders have something like a head gasket that has to be replaced once you open it up? As I mentioned, I doubt there will be any parts for this.
I believe it would be better to try the motor–at least at this point the compressor will pump up!
I’ve not taken this model pump apart Charles, so my response is general. Yes, there will likely be a gasket inside the pump that will need changing. As far as the valves go, you would be looking for anything that looks wonky… broken part, sticking reed etc. I cannot be specific as I haven’t looked inside one. Yup, get the motor checked out first.
I am sure its one of the two capacitors, please tell me where I can order them from?
model number BTM56RB34D2M
As noted on this site: “You are here: Home / Is The Compressor Start Capacitor Working?
Is The Compressor Start Capacitor Working?
This is page three about troubleshooting a Craftsman air compressor that will not start and this page focuses on – is the compressor start capacitor working?
If you want to review the steps from the beginning, here is page one on figuring out why your Craftsman air compressor will not start.
What in heck is a start capacitor?
It’s a device (or sometimes two) normally found on the exterior of a compressor motor, often covered in a metal shroud, near the shaft end of the motor. The purpose of the start capacitor is to help the compressor get going. If your compressor motor also has a run capacitor, that one helps to keep the motor running.
Start capacitor cover installed on electric motorThe start capacitor cover on your compressor motor may look the same as the one shown in the photo, or might differ slightly.
As we have been trying to find out why our Craftsman air compressor will not start, in previous pages we’ve traced the power supply successfully to the motor circuit.
If the compressor motor start capacitor has failed, the power supply to the motor stops there, and the motor will not start.
If you are comfortable with doing so, remove the cover of the start capacitor. Your capacitor may look something like the one in the next photo.
compressor motor start capacitorWhen you get the cover off, examine the capacitor. We are expecting that you have pulled the compressor power cord at this point. Please be careful not to touch the capacitor terminals as a capacitor is a high discharge device, and you could get quite a jolt from the power that’s stored in it.
Look for discoloring, blisters on the outside of the capacitor body, connected terminals that don’t have a lot of corrosion on them, anything that would give you the impression that all is not right with the capacitor.
Even if the motor capacitor looks good, you will still want to check it to make sure that it’s working properly. Please see the embedded video about “How to Check Motor Start and Motor Run Capacitors”
Replacement compressor motor capacitor
You will, unless the label is worn off, be able to see writing on the side of the capacitor. It will show a rating in MFD (mircro-farads) and a voltage range.
As long as you acquire a replacement motor capacitor that has the same MFD rating as the old, and the same voltage range, and you can connect the terminals, then you can use that capacitor, regardless of the shape or size. It’s best to get one that fits inside the existing capacitor cover, of course.
If you cannot see the writing on the side of the capacitor, then it’s time to check out the motor specs to find what capacitor is needed, and you can use your search browser to query what the capacitor is for such and such a motor HP, with xxx voltage etc.”
I have a 5hp Devilbiss ProAir Model PRF5530, 30 gal tank. The compressor has worked fine for about 17 years with no problems. A couple of weeks ago it started throwing the breaker after running for about 3 seconds. I read your articles. Since it starts fine, I replaced the run capacitor and installed a rebuild kit for the cylinder while I was working on it. It still does the same thing. There is no pressure in the tank, no sparks at the rear when it is starting, everything is drained so it isn’t the release valve. The only thing I haven’t replaced is the start capacitor. Since it starts up fine, I didn’t think it was the problem. Any ideas? Thanks,.
“throwing the breaker after running for about 3 seconds.” this suggests the start cap is the issue. Check it out, will you, and let us know?
Finally got the start cap. I was only able to find ONE contractor that could get the start cap from A.O. Smith. No one else had it. I contacted at least 8 different supply houses. Finally found CSH Electric on-line. It cost about $33 which was a lot higher than the other caps I found. The running cap was only $9. Anyway, I put it in last night and it didn’t help at all. Everything else that I plug into that outlet works fine so I know it isn’t the outlet or the wiring to the breaker box. I’m really out of ideas. I’ll probably see if I can find a small-motor repair shop around town and see if they can track the problem down. Thanks.
OK. I’ll order a new capacitor and install it and see if that fixes it. By the way, your video shows the start cap on the outside of the motor. Another site I was looking at said that the start cap was the one inside the rear cover. I replaced the one on the top of the motor. I thought that was the run cap. I’ll get a new one to replace the one in the rear of the motor and let you know what happens. Thanks.
Different compressor motors have different capacitor locations. Some fractional HP motors may even have the cap as part of a circuit board.
Also, I ran another test after posting the above question. I loosened the top air line that connects to the head cylinder on top and moved the air line out of the way. I then attempted to crank it. I felt the air coming out but after 3 seconds it threw the breaker. I reset the breaker and placed my thumb over the head port and tried to crank it. It threw the breaker immediately. I’m guessing that is due to the back pressure my thumb caused.
I have a Ingersoll rand 200 liter single phas. AAttached to a socket in the wall. Used it for good couple of jobs, now it just cuts power after a few seconds of starting and trips the breaker in the house. I use it for sandblasting. Is it possible that maybe the aluminum oxide has some how gotten into the movements?
When the motor runs in the starts for few seconds its fine, then it starts to slow down and trips
Bill, see the troubleshooting page on this site about testing your motor capacitors, and please do so. The compressor symptoms suggest to me that this might be the problem.
My Rigid electric wheel borrow type compressor circuit breaker trip’s around 60psi, any idea what the problem could be ?
Whether or not it’s an electric compressor on a wheelbarrow or not, has no bearing on the circuit breaker tripping, I expect. Are you saying that the circuit breaker in the supply panel trips, and not the breaker on the compressor? If it’s the former, I’d wonder if your extension cord is under sized for the distance from the source to the compressor?
Hi, my craftsman air compressor has worked fine for years and now it blows the fuse as soon as it starts to run. It’s a single cylinder oil free 5 hp max 1.7 hp running 30 gal compressor. 120V 15 Amp. It’s plugged into a receptacle in my garage. I have unplugged it and my fuse is fine so I know it’s the compressor. Where would I find the capacitor(s) and how do I test them? I love to tear stuff apart but I can’t afford to guess with this. I use it all of the time. Need it back up and running asap. Doesn’t matter if tank empty or full, it’s currently empty. Should I look at the motor part itself of first should I look where the electrical cord goes into the box. Model 919.165570
Boz, all the info you have asked for is already available on the pages of this site. No point in retyping it all here. Have a look, and if you have a specific question – other than those that are already answered, please add a comment here.
Capacitors tested fine. I was told by a technician that most likely the bearings are bad causing the inside to touch the windings grounding it out. Electric motors are far from cheap! Holy crap batman!!!! For the price of that I might as well spend a couple bucks more and get a whole new compressor and keep this old tank for storage.
I have 25 gallon husky belt drive air compressor not sure old it is as it was given to me by a friend. It’s been plugged into an outlet with a 15 ft extension cord that runs my garage door and lights for 10 years which is a 15 amp breaker last weekend when tried to start back up it tripped the breaker so I took the belt to be sure it’s not the compressor itself and it still trips took the back cover off the motor and tried cleaning the contact in side still trips I’m at a loss. the motor does have two capacitors. Any suggestions?
See the page on this site about testing the start capacitor. That would be our first step… that, and losing the extension cord completely. Your power supply is marginal even when not being compromised by an extension cord. Move the compressor to the socket and plug it directly into the outlet. Use a longer air line to get air to your tools.
I have a HuskyPro 26 Gal oil lube compressor, when the compressor starts to re-fill I hear the pump cycle about 3-4 times, then it will stall and trip the breaker. I have already replaced the unloader, but that didn’t help. I’m not using any extension cords, and when it is very low pressure, the motor will fire up (but struggle) but then continue to fill up the tank to 145psi or so. the motor already has been reconditioned once (I’m assuming, as the word recon is scratched into the larger of the 2 capacitor bulges on the motor)
If you are sure that the unloader valve is working, and you have not added any load to the power circuit that is feeding the compressor, our recommendation would be to check the start cap.
So, I’ve replaced the unloader, and both the start and run caps… sadly, it’ still stalling on refilling the tank. It will fill the tank from empty just fine, just refilling the tank is where it stalls out. when I let it fill all the way up without stopping it, I can hear the unloader release the pressure, I don’t think it does when I turn it off before it hits it’s full pressure. (I’ve never had an issue with it doing it this way in the past)
Is it fair to say that the compressor works well until there is back pressure from the tank? You’ve checked most of the necessary things to check, yet we wonder if the problem is caused by a wonky tank check valve that prevent free flow of air into the tank, thus overloading the motor circuit? We would remove, clean and / or replace the tank check valve next. If that doesn’t resolve the issue, then it’s pretty much got to be a high pressure valve that’s blocking flow into the tank line as back pressure grows, or it’s the compressor motor itself that has a problem.
I have a dewalt 30hp compressor it fills up fine then when I start to use it and it starts refilling the breaker power pops out and it’s not allowing me to use it again cause the air won’t fill back up please help
Glad to help if we can. What have you checked? Did you read: http://fix-my-compressor.com/compressor-trips-the-breaker-when-the-pressure-drops/ ?
i have a Mcquay unit and the compressor is very hot, i tried restarting it by flipping the breaker off for two hours per instructions from my super, when i re started it, it was on for about a few seconds and tripped the breaker again.
Please tell us about the power supply to the compressor. Extension cord? Amperage of breaker for the compressor circuit. What else is drawing power from the same circuit and so on. If your power supply is starving the motor, overheating and thermal cutout almost always results. If, however, the power supply is good, and the compressor problem is a new one, that suggests that your motor power supply is compromised, and typically that’s a start capacitor problem.
Compressor pumps up to max air when pressure drops it will not come back on until empty was told 3 phase wasn’t big enough.
Well Ron, a bit hard to be specific as we have no idea of the make or model of your air compressor. The troubleshooting pages about air compressors that won’t come back on themselves will be helpful to you we think, and more specifically, can you tell us if the unloader valve works when the compressor reaches cut out?
My compressor keeps tripping the breaker at cut in. Starts fine after I completely empty the tank. I changed the pressure switch, the unloader valve and the check valve. Still trips breaker. Any other ideas? Again starts fine with an empty tank.
Welcome back, Simon. That the compressor starts fine with the tank empty is pointing to a load issue. You replaced the unloader valve, and you confirmed that it is working, which is a good check to make. As long as the power supply is good, and pump pulley turns easily (indicating that there is no mechanical lock up), then it comes down to only a couple of things. One is that you’ve got a valve in the pump that’s locking up under back pressure, or the motor start capacitor isn’t sufficient for the job, or the motor itself is failing.
I have a 4 hp compressor that starts fine when pressure is low but once it has full pressure and it tries to restart it sounds like it is running fast enough but then blows a 20 amp breaker. It seems to make a vibrating noise on and off, then blows. I already changed the starter compacitor, not the run one.
Not knowing the make or model makes diagnosis a bit more difficult, Kevin. If the compressor starts and runs up to cut out when the tank is empty, and only has problems restarting when the tank has air pressure at the cut in level, we wonder if you have checked to ensure that the unloader valve is actually unloading? Not sure what that is? It’s covered on a page on this site.
I have a 120v 6.3amp 1/2hp compressor with a sf of 1.25. I have a 15amp breaker with a 12/2 ran to the motor starter which is operated by the pressure switch on the compressor. The starter has a relay with and overload set at 8.6amps, with a range of up to 20.2amps. The operating pressure is 60psi and when the compressor drains to be refilled it trips upon start-up. What is happening? Do I need a higher amperage breaker? Change the overload amperage? Compressor screwed?
Well, it may not be totally screwed! 🙂 What we think you may have a problem with is the starting capacitor, or the start run capacitor if it only has one. See the page on how to check the caps on this site, and let us know if that was the problem if you would.
I have a 220v air compressor that has been out of service for over ten years. The electric motor was bad so I replaced it with a new one. It will start off and build to under 20psi and trip the circuit breaker. I can slowly build the air pressure to 80 psi after about a half dozen trips of the circuit breaker. If the discharge tube is disconnected from the compressor, it will run fine under no load and not heat up the compressor or the electric motor. Once I start loading the electric motor the circuit breaker trips. It has a Telemechanique XMP pressure regulator with an unloader valve. The compressor does put out a lot of head pressure, so and ideas what I should check next? It ran fine before I took it out of service and never had any problems. It has been and will be stored in a garage.
Tim, we are assuming that you’ve drained the sump and added the correct amount of fresh oil? The air intake filter is clean? The tank check valve has been removed an tested? That being the case additional causes could be a motor capacitor failing, the valves inside the pump are failing, or a possible mechanical issue with the pump itself. You can see the page on this site about testing the capacitor, and that’s what we would do next.
I wonder if someone can suggest me about a problem i having with my 2hp induction motor air compressor. Last week the compressor shotted down the 15 amps circuit breaker, I turned on the circuit breaker then the compressor did run for few minutes then the circuit breaker shotted down again. Since the compressor can run on 20 amps circuit I connected the compressor to 20 amps circuit and then when the compressor did reach 80 psi shotted down, this time by the protection on the motor itself (the red button on the back of the motor) . I called the compressor company and they told me that it was a problem with the motor and they sent me the motor that i installed today but I have the same problem. The pump turn freely by hand so I, don’t think is a pump problem, the compressor turn of to 80 psi all time but it isn’t a problem from the regulator because any time the compressor stop still has the electric power coming from the regulator (I call ”regulator” the device that stop the compressor when the compressor reach the max. pressure )
Please tell us about the new motor, Stefano. Did it come with a start and run capacitor? Or, are you using the older ones. We think that it could be an issue with the run capacitor on this motor. Please see the page on this site about how to check them.
My new compressor was tripping the breaker on kick-in pressure. My garage only has 2 outlets making an extension cord necessary until I re-wire (although the book says avoid extension cords). My New Porter Cable belt driven compressor filled from 0-135 (kick off pressure). I read this tip page and after going to the hardware store and purchasing a new 25′ 10 gauge contractor extension cord (the big thick ones) everything worked perfectly. Thank you so much for this web page! Hope this helps anyone else who has this issue.
Bob, thanks for the vote of confidence. Glad you were able to get your compressor working properly.
I have 2 compressors, both 110volt. Every time I turn on either of them they trip my indoors breaker. If I turn off all lights, radio, etc, it doesn’t trip. No extention cords are used, just the heavy-duty 5-6ft cord supplied on the compressors, straight into my receptacle. What do I need to do? Larger breaker maybe? Or upgrade wiring to larger gauge? Any help would be appreciated.
We suspect a couple of reasons, Kevin. Have a look at: http://fix-my-compressor.com/lights-dim-when-the-compressor-starts/ , and also at this page: http://fix-my-compressor.com/air-compressor-will-not-start/ . How far is the outlet from the power panel and what is the amperage of the breaker? A larger gauge wire could be useful, as might a higher amperage breaker, but we can’t be sure as we don’t know what yours is now.