Air Compressor Capacitor Question

[Retro Active]

I have a Craftsman air compressor that recently started tripping the circuit. It has a 120v/15a motor. It was running on a dedicated 15a circuit originally. I moved it to a 120v/20a circuit and it does the same. It doesn't trip it every time, but it seems to be happening more often.

I've direct wired the pump and it still trips. This is with no resistance as all of the lines are unhooked. Even direct wired it works sometimes and trips others.

I've replaced the start capacitor and it does the same. Before giving up, I want to replace the run capacitor as it's inexpensive. The run capacitor in the unit now is sealed on top but has three wires coming out, two red and one brown. When purchasing a new run capacitor, should I get one with two different connections on the top or three? The run capacitor is a bit less clear than the start and I'm not sure how it should be wired. The compressor is about 11 years old and the part number for the run cap doesn't seem to be available anymore, though similar capacitors are (40uf/370v).

Thanks.

[Eric Wettschreck]

Without doing an amp draw on the motor, replacing the run cap is just tossing a part at it to see if it will work.

If you're tripping a circut breaker something is pulling too many amps. There's a possibility there is a problem with the run cap, but I doubt it. More than likely you have a motor going bad, or a problem with the compressor itself that's causing the motor to "work harder."

[Macgyver55]

Is the bleed valve that relieves the head pressure working?

If there is still pressure in the compressor cylinder when it tries to start it will have a tough time getting it to roll over the first stroke even with a good motor.

[Tom7227]

Is the bleed valve that relieves the head pressure working?

If there is still pressure in the compressor cylinder when it tries to start it will have a tough time getting it to roll over the first stroke even with a good motor.

I had the same problem as the OP and the repair shop fixed it by replacing the bleed valve.

[low277]

I agree that if your compressor has a unloader valve, I would check that first. Is there a small tube from the head of the compressor to the pressure switch?

Does the compressor trip the circuit during the first few seconds of running or after a minute or two?

[Tom7227]

Mine would trip if I tried to start it with more than 20 lbs of air in the tank. If it was empty the unit worked without a problem, and would kick in as I used it.

[low277]

If you have ruled out the start capacitor and/or the unloader valve there is a very good chance that there is a switch inside the motor, usually on the back side of the armature shaft, it is usually a spring loaded device on the shaft that moves when the rpms increase and this in turn activates a switch which shifts the power from the start winding to the run winding, sometimes this switch will fail, you may be able to replace it or if you are lucky it my be a 2 pole switch with only 1 pole being used, then you could just move the wires to the used pole.

[Retro Active]

Thanks for all the replies. I have direct wired the motor around the switch and removed all of the air lines, so neither the unloader valve nor the switch should be a factor. The motor/pump exhibits the same symptoms as it did when fully hooked up. Sometimes it kicks right in, other times it give about .1 seconds of effort and trips the circuit.

I can't find a direct replacement for the pump itself so that is why I thought I'd throw $20 at it and get a run capacitor. It's a single cylinder, oil-less pump and I haven't found anything yet that would look to be a reasonable replacement. I hate to buy something new given the tank is in good shape.

[Rick G]

There was a recall on some of the Craftsman compressors either last year or the one before because of some electrical issues. It would be worth it to see if your model was one of the ones with problems.