Sanborn Magnaforce 104B200-22 compressor intermittently trips circuit breaker on startup

by Erk
(Sacramento)

I am trying to revive an old Sanborn Magnaforce 104B200-22, 2hp, splash lubricated, 110v.


Sometimes the compressor works perfectly, but on occasion when the compressor switches on (either initially by me, or automatically because it's in use and is low on pressure) the unit hums with no startup.

If left this way it will trip the breaker after a few seconds. I've already tried replacing the unloader valve/pressure switch assembly and it didn't help. From what I've gathered online I'm considering the "start capacitor" next, but frankly, although I'm an auto mechanic I have almost no AC experience. I have a Fluke 88V so I may have the necessary tool to diagnose. Any help or advice would be appreciated.
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Erk - two things.

Empty the tank and then try to start the compressor. Did it start? If so, let it run up to cut out pressure and monitor the unloader valve to be sure that it is working. See that page for details.

The other is, see the page on this site about how to test your capacitors.

Cheers,

Bill

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Dec 17, 2012
No progress
by: Erik

I've now replaced the unloader valve/switch combo and the start capacitor. Neither have given me any success.

The problem doesn't seem to depend on air pressure in the tank, it happens when the tank is empty or full.

The compressor side seems to turn with a reasonable amount of resistance, and I tried changing the oil. So I'm guessing the electric motor must be bad internally? Anyone have anything else to check? I don't think this compressor is worth the investment of buying a new electric motor. Thanks

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Coleman Sanborn compressor will not stay running?

by Carlos
(Live oak, ca)

The air compressor will start up fine if the tank is empty.

After it reaches 50psi the pump stops but the motor continues humming and trying to turn over until it pops the reset.

I have read some of your other postings and I decided to change out the check valve.

The compressor continued with the same thing, so I changed out the presure switch. The switch is set at 125 psi shut off, but the compressor continued with the issue and shuts off at 50 psi. Is there anything else that could be causing the problems.

Thanks you,
Carlos
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Hi Carlos...

What you are saying suggests you have a power problem with our compressor.

Give me some details about your power supply please as a comment here.

Oh, and run the compressor one time without the intake filter just to make sure that it isn't a plugged intake causing the problem.

Cheers,

Bill

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Sep 18, 2012
Power source
by: Carlos

The compressor is a 6.5 hp, 230 volt and I have it connected to it's own breaker. I had an electricen look it over, a few weeks ago and he said it was fine. I also removed the filter like you said, but was unable to start the compressor. When i disconnect the Unloader valve or the check valve line from the pump the compressor turns on. I check both lines and air flows threw fine.
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Thanks for the added info, Carlos.

When I said a power problem, I meant the power supply, and I also meant that it could be the power generating capability of the motor.

Good that you have a secure electrical power supply.

That the compressor is stopping under load, in your case around 50 PSI, suggests first, that the run capacitor is faulty, and if that turns out to be OK, then I suspect the motor itself.

See how to check the caps on a page on this site.

Or, when you had your electrician check things out, he did a motor check too?

B.

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