GeneratorAC weird problem... stumped

[aaron_o_]

Hey guys long time lurker, still somewhat new to motorhomes, first post, go easy on me. 🙂

Here's my issue, bear with me, Well first, RV is 2000 Gulfstream SunSport, diesel pusher on Spartan chassis.
Onan diesel 7500 generator. Runs fine, and had it checked and was told it was "100% perfect", he put it on a load bank and ran 50 amps for 10 minutes, worked flawlessly. I wasn't there, but he's a reputable generator repair place as far as I understand. Now, it'll run the water heater fine, I don't know what kind of load those pull, but I'm sure it's not too light.
Here's the problem... when I try to run an AC unit, either one, it runs at first, then you can hear the compressor kick on, then after a short period of time, could be 15 seconds, could be 45, you hear the compressor "kick out" and then the generator revs high for a short period then returns to idle. Repeat this cycle as many times as you like. It will just keep doing this.
Here's the kicker... both units, both separately and together, run fine on shore power, whether it be Georgia Power or my Honda EU6500 quiet generator. All weekend long.
Thinking it could be the switch, I first cleaned the contacts, no help, then swapped the inputs. So the generator was actually feeding in where the shore power would normally be feeding into the switch. No help.
Then I ran a totally separate wire set(stole from my 220 welder extension cord) direct from junction box in front of drivers feet, back through cabin, into input to switch in back. I had 121-123 volts into switch and out of switch. Also had this with coach wiring, forgot to mention that earlier. It does drop a second when compressor kicks on, I figured that was normal and expected.
I also tried the Supco hard start capacitor on one of the units with no help. The units are old, but appear to work fine on shore power, so I've somewhat ruled them out, but not totally.
I'm no electrical guru, especially RV systems, but I'm not your average dummy either. I may have left something out and hope it's something totally simple I'm not aware of with RV's, so give me your thoughts and/or questions and I'll answer them as best I can. Any help is appreciated. I will take it to someone if I have to eventually, but I'm afraid to take it just anywhere and hear the horror stories of people just shotgunning on the customers dime. I can't afford that.
Thank you in advance.

[aaron_o_]

Thanks, just found that also. Appears I have stator/rotor setup, no rings to clean. Any other ideas? The unit is not blinking any codes. Man this sucks. Haha! Going back out to reassemble I guess.

[donkeydew]

http://www.twinslan.net/~n0nas/manuals/onan/981-0522%20Onan%20HDKA%20(spec%20A-M)%20Diesel%20RV%20Genset%20Service%20manual%20(06-2010).pdf

[aaron_o_]

OK, pulled top cover off since I didn't see any easy access to any cooling slots. Maybe I'm missing something, but once the cover was off, I don't see what I was expecting, and no cooling slots. I remember on my propane Onan seeing that area plane as day, but not on this one. For clarification, this is the Onan Quiet Diesel 7500. All I see when I open it up is the big centrifugal type fan between control module box and what I would call the generator section. But, the generator section is just a big block of steel with windings in front of and behind it. You can see the starter ring all the way behind it. Without some massive disassembly and probably pulling the unit, it doesn't look like you're getting in there. I can't see any type of rings like I did on the older propane one I used to have. Any more direction would be great. Supposed to leave Saturday and I have a pile of stuff in front of the rv now. Hah! Such is life, especially mine.
Thanks again.
Oh, here's the model number if it helps any or if someone has manuals...
7.5HDKAJ11451D
S/N J990 000244

[aaron_o_]

Jim@HiTek wrote:
My question would be about the service you got on the genset. Did the shop actually burnish the rings like they should...on a 16 year old genset?I don't believe so, just ran the test and called it good.
Here's my thinking: If the rings are dirty with corrosion and accumulated age related filth, or if the 16 year old brushes are dirty, they could be throwing tons of noise on the AC line. While a resistive 'load bank' would not be affected by that noise, sensitive electronic devices, along with capacitors in the AC, could be.Makes total sense. While I did check the frequency(dead on), I did not have an oscilloscope to see how clean it was, didn't really even think that far into it. Great idea! Thanks!

Hopefully I can get to them(air slots and rings) without too much trouble. I can't remember seeing the slots on this one. I'm sure it is though. I'll try this this afternoon and report back.
Thanks for the help guys!

[aaron_o_]

KD4UPL wrote:
How long has it been since the fuel filter was changed on the diesel gen?

It was one of the first things I did just as normal operations after I make a purchase. Now, maybe a year ago, but probably 10 hours ago on the meter, at the most.

[Jim]

My question would be about the service you got on the genset. Did the shop actually burnish the rings like they should...on a 16 year old genset? If it's not shown on the receipt, you should do that. A 12" long, 1/4" square stick of wood with a strip of fine sandpaper glued or stapled to the end of the stick is all it takes. Start the engine, jab the stick in the air flow slots and go to town on the rings.

Here's my thinking: If the rings are dirty with corrosion and accumulated age related filth, or if the 16 year old brushes are dirty, they could be throwing tons of noise on the AC line. While a resistive 'load bank' would not be affected by that noise, sensitive electronic devices, along with capacitors in the AC, could be.

BTW, you have already done a lot of excellent testing. You'll do fine in your RV if you keep that up...

[ScottG]

aaron o. wrote:

ScottG wrote:
For some reason, your not getting the surge current you need from your Onan. Could be the gen but also could be a bad connection, damaged wire or resistance in the transfer switch or, someplace else.
I bet if you could bypass all the wiring from the gen to the AC, it would work fine.

I could try that with the front ac, not sure if I have enough to reach the rear, but that's a good idea also. Thanks.
I agree I'm getting resistance somewhere, but why would the Honda run it fine through all the same wiring after the switch?

Another thought... Would house battery condition have any affect on this?

Perhaps it's before the switch.
Not sure if a low house battery would cause the issue. If it was discharged and the converter had to go into bulk charge mode it could cause problems but I cant imagine the gen being that borderline.

[KD4UPL]

How long has it been since the fuel filter was changed on the diesel gen?

[aaron_o_]

ScottG wrote:
For some reason, your not getting the surge current you need from your Onan. Could be the gen but also could be a bad connection, damaged wire or resistance in the transfer switch or, someplace else.
I bet if you could bypass all the wiring from the gen to the AC, it would work fine.

I could try that with the front ac, not sure if I have enough to reach the rear, but that's a good idea also. Thanks.
I agree I'm getting resistance somewhere, but why would the Honda run it fine through all the same wiring after the switch?

Another thought... Would house battery condition have any affect on this?

[aaron_o_]

msturtz wrote:
Did the AC run properly on the welder wiring?

No

[msturtz]

Did the AC run properly on the welder wiring?

[ScottG]

For some reason, your not getting the surge current you need from your Onan. Could be the gen but also could be a bad connection, damaged wire or resistance in the transfer switch or, someplace else.
I bet if you could bypass all the wiring from the gen to the AC, it would work fine.