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Old 09-17-2021, 09:56 PM   #1
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Cummins Onan Marquis 7000

Looking for help with my Marquis 7000 generator. It runs but doesn't power my air conditioning in my 1999 Newmar dutch star 3884. The air conditioning runs on shore power. I have replaced both breakers to no avail. Not sure how to test the Automatic Transfer switch and would be willing to convert to a manual plug in if necessary to avoid replacing the switch for big dollars. Reading many posts and watching YouTube videos but not alot for my problem or unit
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Old 09-18-2021, 06:11 AM   #2
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Is the a/c the only item that does not work when running the generator?
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Old 09-18-2021, 01:54 PM   #3
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I think so. How can I confirm that its not drawing off the batteries?
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Old 09-18-2021, 02:37 PM   #4
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Originally Posted by Dutch1999 View Post
I think so. How can I confirm that its not drawing off the batteries?
Wow! You need to be more specific in describing your problem if you want help.

I have this same generator. I also have two air conditioning units (A/C). I can run both A/C on 50 amp shore. I can run both A/C on the generator.

When not connected to shore power or the generator, I can not run either A/C because because inverter supplied 120 vac drawing from the batteries does not supply large loads like A/C.

Sometimes on my Onan, it will momentary slow down enough when an A/C loads to trip a low frequency protection feature. My Onan will continue to run but not produce 120 vac.

When this happens, the inverter supplied 120 vac will still have power.

Yes it is confusing.

Here is what you need to do. Get a outlet tester for less than $10. When on shore power check that all of your outlets have power and properly wired. Make sure large loads like A/C and hot water heater work.

Then disconnect from shore power. Use your outlet tester to learn what outlets are powered and which are not. Leave the tester in an outlet not power by the inverter.

Start your generator. After a short time delay, you should have 120 vac on all your outlets.

Let us know what you find.
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Old 09-19-2021, 07:16 AM   #5
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Quote:
Originally Posted by Dutch1999 View Post
Looking for help with my Marquis 7000 generator. It runs but doesn't power my air conditioning in my 1999 Newmar dutch star 3884. The air conditioning runs on shore power. I have replaced both breakers to no avail. Not sure how to test the Automatic Transfer switch and would be willing to convert to a manual plug in if necessary to avoid replacing the switch for big dollars. Reading many posts and watching YouTube videos but not alot for my problem or unit

What transfer switch do you have?
If it's like mine, replacing a faulty contactor or a circuit board is a cheap alternative. Those are about $80.00 each.

On my Esco ES50M-65N it's easy to diagnose (once I get there as it its mounted to a difficult to reach location).

On the pic below shore line input is on top top right and generator input is bottom right (ALTERNATE).
The output side (LOAD) is tied together on the left side from shore contactor to the same posts on the generator contactor where it says "Do Not Use".

When the shore power is used (generator off), you should see 120V between Hot one and neutral. Same between Hot two and neutral. And nothing on the generator input side.
Then on the output (Load) side, you should have the same 120V between Hot one and neutral. Same between Hot two and neutral. And obviously the same on the generator contactor output side since they are tied together.

When shore power is off and generator is on, you should see the same input and output 120V readings on the bottom contactor: 120V between Hot one and neutral, 120V between Hot two and neutral.

If the generator input terminals have no power, you probably have a tripped circuit breaker in the generator or bad contact (maybe corrosion) on the generator cables.
If the generator input has power but not the output, then the contactor is bad. Or maybe the circuit board not making the switch. You can get both from Esco USA.


You can see a circuit board on the right side tied to both contactors. That controls the switching.
If both on shore power and generator are running, only one of them should pass current thru to load side. Typically it's the generator but could be either one.
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Old 09-19-2021, 07:44 AM   #6
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IF (big IF) you are safe working around 120 VAC:


With shore power unplugged, generator OFF, AGS OFF, inverter OFF, remove the lid to the ATS.


Identify the wires IN and OUT. There will be two on the IN side-- shore power and generator. There will be one on the OUT side, going to the main 120 VAC breaker box. Make sure all connections are clean and tight. No signs of burned wires.



Start the generator.



Check on both IN and OUT sides as follows:


black to white= 120 VAC
red (or alternate color) to white= 120 VAC


Tell us what you find.


Do NOT just throw parts at it. Determine what is wrong and fix that.
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Old 10-02-2021, 09:20 PM   #7
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My transfer switch. Sorry for the lapse in my dilemma but the DC on my coach was not working suddenly and I had to troubleshoot and replace the battery disconnect switch. Back to getting the generator working. I replaced both breakers. I plan on testing the outlets to find out which are shore power and which are not. Appreciate your patience during my absence on this issue. I am beginning to believe that electrical issues are an RV's biggest opportunities.
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