Community Forums

baraff · 08-19-2016, 04:02 PM

I have an Onan 4000 Microquiet (gas). Last week my air conditioner compressor fried and when it died it knocked out power to the generator, which was running at the time. No circuit breakers tripped, either in the RV, or on the generator itself. Resetting the generator breaker (which did not appear to be tripped) does not resolve the issue.
The RV shop I went to suspects the brushes are bad. Would a shorted circuit blow out the brushes or might it be more ominous? Any thoughts or procedures to troubleshoot this unit?
Also concerned as to why no breakers tripped, a/c, Main, or generator.
We're leaving on a trip soon and really need this generator to work!
Thanks for any help you can offer.

MtnTrek · 08-19-2016, 06:03 PM

No expert but a thought.
How many hrs. on the generator? Those models 4K MQ seem to need brushes etc. around 500-700 hrs. may have been a coincidence. The leads can get flakey prior to the brushes being totally spent.
Some can go out of tolerance in between exercise cycles.

Be well.

baraff · 08-19-2016, 06:06 PM

About 250 hours on generator. I understand it's a big job to change these out as you have to drop the genset from the motorhome.
I hope I didn't burn up the armature wiring, it concerns me that none of the breakers tripped.....

tderonne · 08-19-2016, 09:09 PM

So it runs, but nothing works?

I've read that the generator will shut down if it doesn't see an output voltage. I'd search around and verify that. Then I'd get out my volt meter and check for voltage at the breaker.

hawkeye1995 · 08-19-2016, 10:32 PM

Might take a look at the switch box? The one that switches from shore power to gen power. I would say that may be fried.

MtnTrek · 08-19-2016, 11:07 PM

^^^ you mean the transfer switch?
Re-reading the OP, I perceived him to say he'd visited a shop and they'd determined the brushes were gone.
So, yeah. OP You've eliminated the transfer switch right? Is there potential from the generator to it? As someone posted if it's not producing the rated potential it may shut down the engine and issue a fault code. There may also be a fused exciter circuit and PC card in there too. You should be able to find a schematic and or a trouble shooting guide on-line. But I think they have to pull the flywheel to get to the brushes.

baraff · 08-20-2016, 11:01 AM

Quote:

Originally Posted by MtnTrek

^^^ you mean the transfer switch?
Re-reading the OP, I perceived him to say he'd visited a shop and they'd determined the brushes were gone.
So, yeah. OP You've eliminated the transfer switch right? Is there potential from the generator to it? As someone posted if it's not producing the rated potential it may shut down the engine and issue a fault code. There may also be a fused exciter circuit and PC card in there too. You should be able to find a schematic and or a trouble shooting guide on-line. But I think they have to pull the flywheel to get to the brushes.

No transfer switch. This is a class c, has a plug receptacle; plug cord in for generator, remove for shore power. Everything works on shore power (except air conditioner which is fried).
Presumably they checked the receptacle box, but I will check to see if the wires are burned off when I get it back from the repair shop. They have recommended I take to a generator repair shop for further diagnosis.
The only fault code is a solid red light on the generator switch, which indicates no power. Generator engine runs fine and does not shut down by itself.