Onan Cummings RV QG 5500 generator issues

[Drscott1959]

2016 WB 35B VISTA Been plugged into 50 amp service here at the house for a couple weeks. Decided to start generator just to let it run for a while with a load. Took cover off and noticed a cable connector was split into. Simple fix, put new connector on cable and started right up.

But my front air will not run on just the generator. The back air does, but not the front. BOTH BREAKERS SWITCHES are on back at the generator. My other outlets are good up front such as TV and microwave. If I turn generator off, plug back up to shore power, both front and back AIR works fine.

All other breakers inside MH are good and not tripped. It seems sluggish or slow that maybe it’s not recognizing being switched from shore to generator. I let generator run for 15 mins or so then tried turning on front air, but nothing. It wont come on. What am I missing here?

Thanks for the help and suggestions.

[creativepart]

I'd suspect the Auto Transfer Switch. It is generator priority... so even on shore power when you start the generator it switches to generator power.

Inside the ATS are two "contactors". These are big high power sliding switches that have a solenoid to lift a bar to contact the two lines of power. One contactor is for shore power and the other for the generator. Each one has two contacts for each line.

Bugs and sometimes arcing can lodge on a contact and keep it from connecting both lines completely.

BUT, don't take this as a slam dunk answer though. It can be any number of other things beside the ATS.

The 5500w genset can run both A/Cs but not if it's also charging the batteries and heating water in the water heater. So, check that the WH is not on electric. Also check the OnePlace monitor for how many amps are being seen when the gen is running.

[meyeet]

On my 2010 Vista, there is a switch to select if the A/C runs on External Power or the Generator. It's in a cabinet beneath my fridge where the power panel is. Not sure if yours is the same but might be worth checking for it.

[Drscott1959]

Thanks so much for the reply. I completely understand what your saying, but since the back air comes on with generator running would that not rule out issues with the ATS? Just a FYI….the HWH is not on and I have everything else off.

Thanks again.

[Bones2003]

Because the generator is supplying power to the rear AC could still mean that the ATS has a problem. Because you have a 50A RV, you have two power legs (or lines) that are each 50A. Usually the front AC will be on one leg and the rear AC will be on the other leg. So it could be that the ATS is only correctly switching one leg.

You might check to see if any other outlets or appliances are working or not. It may not just be the outlets in the front.

[Bones2003]

From this link, you can find the wiring diagrams for your RV. You have to select the year and model number based on your serial number.

https://www.winnebago.com/Files/File...ram/Wiring.htm

[dkoldman]

You laid out info nicely, but more specifics are needed.


i.e.
When did it last work?
What kind of Power Mgmt System do you haver if any?
Have you tried turning rear AC off and just running the front AC with genny?
Have you verified that you have 120 vac at both inside breakers where the generator power would come in if it were on? I assume you verified the output on breakers at the genny.

But here is the sure fire can't miss.

Measure the output voltage of ATS with shorepower on. Disconnect and measure output voltage again of ATS with generator on. If you then tell me the front AC works with the shorepower; but not the generator, I am gonna say that is impossible. The front AC does not know or care where the 120 VAC came from.

My money is on you having an issue with ATS that may need to be replaced or serviced. I can't see any other way since that front AC gets power from Shorepower with no issue; unless your RV is rewired and Shorepower is NOT wired through the ATS.

[Morich]

Sounds like the wiring for the generator to switch and on to the breakers may not be right but some checking needs to be done.

There are several different versions of that year, make and model, so some guessing until we verify which you have?
Since you have two AC, can we assume this is how your load center lays out with two 50 amps feeding two 20 amps for the AC?

Click to get a better view of snip or go direct here.

This is a section of this drawing from sheet 6, way down at the bottom:
https://www.winnebago.com/Files/File.../000181048.pdf

IF I'm right on the guess and this matches what you have, I would suggest checking at the breakers for front and rear getting good 110 AC leaving the breakers for both front and rear while the generator is running.

I suspect there is a problem getting power from the transfer switch to the breaker and you will NOT find power on the first 20 amp breaker at left side when on genset but will when on shore power.

Following that guess, I might next want to open the transfer switch to check for loose or burned wires as they seem to be a trouble point.

[Morich]

If it turns out you are missing one leg of the 110 AC that feeds from the genratorto the front AC, This is what I see needing checked.

We can say one leg gets from genset to brer to AC as the rear works and both work on shore power, that is the blue line.
But supect is whether the 110 AC is getting out of the gen tothe transfer switch. Does it then also go through the transfer switch as the red line and get to the lines going out to the breakers?

The screws at the red marks are something that get loose and start heating/burning, so look them over and tighten while there.

Careful! Remember it's okay to look but don't touch until you pull the cord and also kill the generator!

[dkoldman]

Originally Posted by Morich

If it turns out you are missing one leg of the 110 AC that feeds from the genratorto the front AC, This is what I see needing checked.

We can say one leg gets from genset to brer to AC as the rear works and both work on shore power, that is the blue line.
But supect is whether the 110 AC is getting out of the gen tothe transfer switch. Does it then also go through the transfer switch as the red line and get to the lines going out to the breakers?

The screws at the red marks are something that get loose and start heating/burning, so look them over and tighten while there.

Careful! Remember it's okay to look but don't touch until you pull the cord and also kill the generator!

That picture is worth 1,000s words and says it all. One trend I have noticed is Thor Motor Coach and Onan Cummings generators get blames a lot. I am sure they have there fair share of problems like anyone else, but often times when al the layers get pulled back, they are not the root cause. I hate Marketing anyway, but I would think working in Marketing for TMC or Onan Cummings would be the worse jobs

Remember that project I did a little while ago to feed my Home Transfer Switch off my Onan Cummings RV QG 5500 generator in an emergency. I used the same leg as OP should be concerned with out of the ATS as it also supplies my #2 AC.

[Drscott1959]

I really appreciate your reply. Here is a little update. I took the cover off the ATS and didn’t really see anything that looked out of place. I did snug up a couple of the connector screws but I would not say they were lose.

Started generator. The fan will run on the front air but not the compressor. All other outlets are working fine during this time. So I turn the front fan off and turn on rear air. It kicks on immediately but instantly the generator starts a constant laboring. As soon as I turn the back air off, the generator starts running smooth again.

Turned the generator off, plugged up to 50 amp and both airs kicked on and worked fine. So obviously something is going on.

Again, I do appreciate your help.

[Morich]

That makes it sound like a bit different problem, so I might suggest trying this to see if you can isolate it to one AC or the other.

If you go to the breakers and flip one of the 20 amp which feeds the two AC to off and leave the other on, will the generator run the remaining AC without sounding like it is having a hard time?

If one AC works with generator fine, try turning that one off and the other ON to see how it works with the generator.

The Air cond. only have one power feed for each so this may tell that one has a problem but not the other. That moves the question and problem away from the generator, transfer switch and wiring and more into the one AC which gives trouble!

As a first guess without more testing, it sounds like one AC compressor is having trouble starting and draws more current, causing the generator to struggle?
There are "start capacitors" which are made to help start the compressor and may be the problem.

[Drscott1959]

Again, your help is greatly appreciated. What’s confusing me ( and that’s not hard, I’m about a 65% person on fixing things, u tube is a dangerous thing ) is that both airs works fine on 50 amp shore power. I will try these things you have suggested.

Have a great day.

Doug SCOTT

[dkoldman]

Originally Posted by Drscott1959

Again, your help is greatly appreciated. What’s confusing me ( and that’s not hard, I’m about a 65% person on fixing things, u tube is a dangerous thing ) is that both airs works fine on 50 amp shore power. I will try these things you have suggested.

Have a great day.

Doug SCOTT

It can be dangerous if you not use to working with voltmeters, but you should really check the voltage at all of the legs involved in that diagram provided.

i.e. confirm 120vac out of both breakers atr genny or just jump that to confirm 120 vax at both legs into ATS.

Then check both legs output of ATS.

This is where I was saying earlier the 120vac output from ATS will not know or care where the power came from, genny or shore.

All you describe and with no real empirical data suggest you may not be getting proper power from the generator side of wiring. You really need data to verify.

I have seen generators run, but not produce power, and I have also had situation where my ATS had to be replace under warranty. I was really glad, because I thought my genny was gone.

What I do find odd, is that I think you have said when genny is running, everything else works normally except that one AC? If true, find a plug on the same leg as that AC and plug in a compressor or heavy duty vacuum cleaner.

[Drscott1959]

JUST A FYI….did everything you suggested and kicking off one breaker or the other did not change the generator one way or the other. It did do something a little different tho.

When I first started the generator and then turned on the back air, it took maybe 2 to 3 minutes for the display board to light up or kick in or recognize the Generator was running. It seems like it’s have a hard time determining switching from shore to generator. Which could lead us back to a bad ATS maybe? I’ve reached out to a local RV repair man. Maybe he can bird dog it for me and get corrected.


SADLY,ITS NOTHING MONEY WONT TAKE CARE OF

Don’t feel like you need to reply. It’s the weekend and I’m sure or hope you got better things to do.

When or if I get corrected, I’ll let the group know for future references.

[Drscott1959]

II’d love to get your opinion on this.

So I started the Generator and let it run for maybe 30 minutes with no load.

Then I put on the back air only and the generator kept running smooth without laboring.

After about 30 more minutes, I kicked on the front air and they have both been running at the same time with no issues or laboring on the generator.

Now yesterday, I could not get the generator to run both. But I was trying it just a few minutes after I 1st started the generator up.

Was I rushing things?

Thanks again.

[Bones2003]

You might be rushing things. When you start the generator, it should run for a few minutes to start to warm up before putting a load on it. Because of this, most ATS have a built in timer that delays switching over to the generator. I think on my ATS, that timer is adjustable by moving some jumpers on the circuit board in the ATS. In addition, most air conditioners have a different timer that delays for a couple of minutes to prevent damage to the compressor.

[dkoldman]

Originally Posted by Drscott1959

II’d love to get your opinion on this.

So I started the Generator and let it run for maybe 30 minutes with no load.

Then I put on the back air only and the generator kept running smooth without laboring.

After about 30 more minutes, I kicked on the front air and they have both been running at the same time with no issues or laboring on the generator.

Now yesterday, I could not get the generator to run both. But I was trying it just a few minutes after I 1st started the generator up.

Was I rushing things?

Thanks again.

way to stay at it.

When you said "When I first started the generator and then turned on the back air, it took maybe 2 to 3 minutes for the display board to light up or kick in or recognize the Generator was running."

That sounded like my unit part of the power management system, but I let it go as you were bringing in a RV guy.

But yes, here is what I think I remember from my genny startup, but somewhat may correct some detail of the same.

1. Genny starts up
2. Takes about 1 minute and my Power Management board lights up
3. The system determines if I have 50 amp or 30 amps. If 15 amps; I have to tell it that
4. All of the small stuff comes on immediately
5. Another 2 minutes may pass and AC#1 comes on; or #2 if it is only one set for ON - It will start.
6. Both units will start eventually, but there is some delay and I believe the AC units also have a delay for starting and stopping to protect the compressor.

One other thing, don't discount that extra torqueing you did? Loose screws the way you may have been thinking may have meant too late because that is what you see when you have a fried ATS. You have dun to the extent you have re-torgued and that is good PM

[Morich]

Whether it is the current question or just another point to keep in mind, the small details can matter.
One of those small details is that we don't want to start an air cond. ,shut it off and then start it again right away. Some have delays built in, some not so much, so it is good practice to just get used to letting the compressor "rest" before restarting.

When the compressor runs, it builds up high pressure and that pressure makes restarts really hard as the compressor has to work against the existing high pressure if we don't give it some time to gradually release that pressure.

This applies to both RV and home units, so worth keeping in mind as either place may jump up to bite us. Maybe it only blows a breaker which we have to reset or maybe it lets various wires get hotter than they should and shortens the life of things?

Just better not to put the extra strain on things!

[Sullivanclan]

Lots of great information.