33 gal Craftsman compressor keeps tripping the breaker?

Categorized as Air Compressor Troubleshooting 2 Comments on 33 gal Craftsman compressor keeps tripping the breaker?
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A 33 gal Craftsman compressor keeps tripping the breaker? How come? A visitor wrote in, I have a 33 gal Craftsman compressor that was given to me. So far I have replaced the piston/sleeve set up, and also the valve plate. It now builds pressure, but for some reason it also keeps tripping the breaker.

It also continues to leak air from unloader valve once it has cut out.This compressor is plugged into a wall, or a brand new generator. Any ideas? Thanks, Norman R.

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Craftsman Sears 2 HP air compressor
Craftsman Sears 2 HP air compressor

Thanks for the question. To recap, typically an air compressor with a pressure switch has a reservoir tank that fills with compressed air while the compressor runs. When the cut out pressure level in the tank is reached, the air compressor motor stops.

When air is used, or if there is a leak, the pressure in the tank drops to the cut in pressure. The compressor starts and fills the tank back up to cut out pressure, and then stops again, waiting for a pressure drop in the tank to initiate restart. The ON/OFF process is handled by the pressure switch, which often also includes some type of unloader valve either on the side of the pressure switch or plumbed in from the bottom to an internal unloader.

The unloader valve is there to dump air out of the pump when the compressor stops. If it isn’t working, that increases the load on the pump, and then the motor, and could prevent the motor from starting. Back to that in a moment.

Air is leaking from the unloader valve

The unloader valve is supposed to leak air all the time the compressor is off, and stop the air “leaking” out when the compressor starts.

If the unloader valve is leaking air when the compressor is stopped, take moment to ask yourself where that air is coming from. The answer is, the tank. And why should air from the tank be leaking out the unloader valve? That’s because the device that is supposed to keep the air in the tank so it can but plumbed to air tools to work them, and prevent that same air from coming out of the tank and out the unloader valve (which as mentioned is supposed to be open at this point) is the tank check valve.

Almost all compressors with unloader valves have a tank check valve to do just that. Keep the air in the tank tank when the unloader valve is open.

It’s almost certain that the tank check valve on your 33 gallon Craftsman compressor is leaking, and either needs to be cleaned or replaced. How to do that is covered on another page on this site so I won’t add all that detail here. Please have a look at the menu to find the page that relates to that, won’t you?

33 gal Craftsman compressor keeps tripping the breaker.

Now, back to this specific issue.

I referred earlier to the unloader valve function, and if the unloader valve didn’t work properly, that it may overload the motor.

That may be one reason why a Craftsman compressor trips the breaker on start up. The motors on these smaller air compressors are marginal at best in terms of their power capabilities, and the power supplied from household current is also typically marginal in electric motor starting based on the relatively low current flow.

Almost all electric motors need a significant “inrush” of current to get the motor started if conditions for starting are optimal. If air is trapped over the piston in the pump due to a non-functioning unloader valve, this will add load and may just add enough load to the motor that it cannot start with the current available, the motors may continue to try to start, may even buzz or hum, and ultimately it will trip the breaker.

So please check and be sure that the unloader valve is working.

If the unloader valve is working as it should, than another cause could be the following compressor part problem.

Is the start capacitor working?

The start capacitor is part of the reason that a marginal electric motor can start at all. In simple terms it gives the motor an electrical boost for a very short time to give the current more oomph to get the motor started. If the start cap has failed that boost isn’t available, the motor cannot get going with the current available in the household circuit, it keeps trying to start, and ultimately that process trips the breaker.

Rather than retype it all here, here is a page on this site about how to test the capacitor. Please have a look, check things out as per above, and let us know how it worked out, OK?

By Ashley Pearce

As a passionate manufacturing and mechanical engineer, I've had my fair share of run ins with air compressors and compressed air systems. With over a decade of experience in the industry, I have both a fresh perspective and time-served hands and mind to help you with your compressor problems (along with our able community!)

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Richard Long
Richard Long
May 20, 2021 3:35 am

i have a craftsman upright air compressor that got turned over. It will run for like 3-5 seconds and kick the electrical breaker. The pressure gauges read 0 pounds pressure. Help will be greatly appreciated.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Richard Long
May 20, 2021 11:37 am

Is your model of compressor oil lubed? Does it have an external or internal pressure switch? Be good if you would add a comment with the model number and a photo of the compressor head with the cover off. Thanks.