Onan 4k Generator shuts down when the A/C compressor Cycles on

[Camper_bob]

Yup.

And I'd be checking the wiring between the AC circuit breaker in the main panel and the AC unit itself (including the circuit breaker itself).

Have you tried bypassing the ATS by connecting generator output directly to the main panel?

You stated that the AC unit runs fine on shore power? Are you getting excessive heat at any of the junctions between shore power and AC unit?

There's a video on Youtube of how to check the various components in the AC unit (start capacitor, run capacitor, etc) with a volt meter and an amp meter.

https://youtu.be/3VckFAXg1CY

But given that the AC unit works fine on shore power, I'm wondering if you're going to find anything there...



Also, how long does the generator "try" to fire up the AC before it shuts down? Is it instant? Or does it bog down for a few seconds, then give up?

[Cavie]

Originally Posted by Camper_bob

Yup.

And I'd be checking the wiring between the AC circuit breaker in the main panel and the AC unit itself (including the circuit breaker itself).

Have you tried bypassing the ATS by connecting generator output directly to the main panel?

You stated that the AC unit runs fine on shore power? Are you getting excessive heat at any of the junctions between shore power and AC unit?

There's a video on Youtube of how to check the various components in the AC unit (start capacitor, run capacitor, etc) with a volt meter and an amp meter.

https://youtu.be/3VckFAXg1CY

But given that the AC unit works fine on shore power, I'm wondering if you're going to find anything there...



Also, how long does the generator "try" to fire up the AC before it shuts down? Is it instant? Or does it bog down for a few seconds, then give up?

If it works on shore power as stated then there is no point in doing that.

[Camper_bob]

Originally Posted by Cavie

If it works on shore power as stated then there is no point in doing that.

I'll defer to your electrical expertise here.

But a question: Could the AC unit work on shore power even with a loose connection in the line somewhere, and you might not notice as much until you start seeing smoke coming from the wires? Whereas the generator will "see" the voltage drop due to increased resistance and cut it off and throw a code?

That's an honest question.

[JimD]

Originally Posted by Camper_bob

I'll defer to your electrical expertise here.

But a question: Could the AC unit work on shore power even with a loose connection in the line somewhere, and you might not notice as much until you start seeing smoke coming from the wires? Whereas the generator will "see" the voltage drop due to increased resistance and cut it off and throw a code?

That's an honest question.

If there is resistance in the line the voltage drop would appear across the resistance and not at the generator. Say the generator was putting out 120 volts at 20 amps but that power was not reaching the AC unit because of the resistance. If you have only 2 ohms of resistance you would have a voltage drop of 40 volts across that resistance (I x R or current x resistance).

If the generator is seeing a voltage drop and throwing an error code because of it, I would suspect the resistance, if present, would be internal to the generator. That could be tested by monitoring its output voltage and adding in multiple loads and watching if the voltage drops off. The voltage should be farely constant up to the generator's capacity.

[2edgesword]

My thinking is if the A/C works on shore power and everything but the A/C works on generator power the issue is the A/C overloading the generator. The fact that everything is working via some power source pretty much rules out loose connections..

[Taylor O.]

Originally Posted by Camper_bob

Yup.

And I'd be checking the wiring between the AC circuit breaker in the main panel and the AC unit itself (including the circuit breaker itself).

Have you tried bypassing the ATS by connecting generator output directly to the main panel?

You stated that the AC unit runs fine on shore power? Are you getting excessive heat at any of the junctions between shore power and AC unit?

There's a video on Youtube of how to check the various components in the AC unit (start capacitor, run capacitor, etc) with a volt meter and an amp meter.

https://youtu.be/3VckFAXg1CY

But given that the AC unit works fine on shore power, I'm wondering if you're going to find anything there...



Also, how long does the generator "try" to fire up the AC before it shuts down? Is it instant? Or does it bog down for a few seconds, then give up?

it seems that it wants to try and cycle, but then the generator shuts down

[Dan50]

https://www.microair.net/products/ea...nt=30176048267

[LexGator]

Originally Posted by Taylor O.

I need help, if anyone has experienced this, I would greatly appreciate a reply.
I have a 2012 Jayco ZX24 Octane Toy hauler with an Onan 4k generator. My current issue is when on Generator power, I start the A/C, when the compressor starts, it will kill the generator.
What I have done so far. The generator is running on fresh, non-ethanol fuel, the spark plug and air filter have been replaced, oil level is correct. A Hard Start Capacitor has been installed on the Coleman Mach Series, 15,000btu (a starting booster).
The ATS (automatic transfer switch) engages on generator, 120v reading. The electrical panel has had all of the circuit breakers turned off, leaving only the a/c breaker active. No electrical draws present. The generator is run to warm up, engage the blower to apply some load to the generator, after 2 minutes, engage the compressor, ATS begins clicking and the generator shuts down.
I have also started the generator, put a full electrical load on the system, all lights on, refrigerator, exhaust fans, microwave, TV, fans, the generator runs flawlessly.
Tested the ATS, when on generator power, 120v registered, on Shore Power 120v. When turning on the Generator, the ATS is a 120v until engaging the A/C, then the power drops to 6v and shuts off.
If on shore power, the a/c system works as designed, cools the camper to ice cold. Everything works as designed.
The generator restarts every time with no delay on restart.
If anyone has any input, I would be greatly appreciate any input

Taylor

I had the same issue - installed an ezstart - problem solved. Wish they put them on at the factory since this is a known issue.

[dogmeat]

as stated, you need to find out what the current draw is on startup. if it is higher than expected, the AC is at fault. if it is within spec, the generator is tripping too soon. bear in mind that shore power has unlimited current available at a stable regulated voltage. it is only limited by the circuit breaker. and thermal CBs (not magnetic) can take a momentary overload like excessive start current and not pop off

[Taylor O.]

Checked the amp draw on the a/c system. While on shore power, a/c system draw was between 10.1-10.7 on 4 different test.
On generator power, tested between 10.5-11.2 on start up draw. A/c system tested within normal parameters For a Coleman Mach 15k unit

[Taylor O.]

Generator is currently at Cummins for professional opinion starting at $175.00. I can’t wait to find out what I don’t know.

[Grumpy]

Originally Posted by Taylor O.

Generator is currently at Cummins for professional opinion starting at $175.00. I can’t wait to find out what I don’t know.

We're all waiting with you.....

[Johnynorthland]

[QUOTE=Taylor O.;904780]13, under voltage from what I can find.[/

Yes, please keep us “posted”!

[royphillips]

I think there is a safely on the generator if it draws too many watts it will shut down. We had that happen a few time if we had other electrical Items that happened to be on at the same time and it was drawing to many watts.

[dogmeat]

the math says he's drawing 1344 watts at start so a 1500 watt genset should be OK with that. of course the 11.2 amp reading mentioned in post 29 depends on if it was taken with a meter that is fast enough to capture the true max inrush current. once the compressor motor starts to turn the current will decrease

[Grumpy]

Originally Posted by dogmeat

the math says he's drawing 1344 watts at start so a 1500 watt genset should be OK with that.

It's a 4000 watt geny.

[dogmeat]

yep, and 1500 is all you need

[2edgesword]

Originally Posted by dogmeat

the math says he's drawing 1344 watts at start so a 1500 watt genset should be OK with that. of course the 11.2 amp reading mentioned in post 29 depends on if it was taken with a meter that is fast enough to capture the true max inrush current. once the compressor motor starts to turn the current will decrease

I'm not sure how you calculate 1344 watts at startup but I'm 99% sure that can't be accurate. A 1344 watt startup means an 11.2A current draw. The running current may be 11.2A but starting current is going to be much higher. One estimate I read for a 15K A/C was 3500 watts which at 120V would be 29A, a more realistic based on the numbers I've seen with my 13.5K btu A/C. That 29A would be for a new A/C. As the A/C gets older the power to start it increases. Couple that with the fact that as generators age they become less efficient and my feeling is still that the A/C startup is knocking the generator into overload mode.

[dogmeat]

well... post #30 he says the start draw was tested and 11.2 was the highest, and within specs. I can't tell you if thats true because I didn't check it. also, as I noted, you need to test with a meter that has a fast enough processor time to read the inrush accurately.

and I agree... that inrush number sounds low.

[Camper_bob]

There's no way the startup amperage is that low, that's going to be running amps. The "locked rotor amperage" on a Coleman 15K unit is 61A.

That's why I was wondering if OP could start his microwave and maybe a hair dryer at the same time while on genny power. If you could replicate the startup amperage the AC unit requires, you might be able to prove out that it's the generator and not something else.

I'm wondering if the generator "hiccups" when lesser draws are applied, and how severe that hiccup is? Mine is in good running condition, and will run both of my ACs just fine (1x11,000 and 1x13,500 HE). And you can hear the generator "hiccup" when I turn on the microwave (I don't do that with both ACs running usually).

OP also mentioned he installed a start capacitor in the AC unit. That SHOULD be helping with locked rotor amperage required at startup.

On shore power, it should be able to pull as much amperage as it needs to start up. At least momentarily, before it opens a breaker. In the case of a generator, the sudden amp draw has to be compensated for with the engine, and it may just not be healthy enough to overcome that sudden kick. Hence why it "tries" for a few seconds and then gives up (so it doesn't cause more damage to the generator or the compressor).

An example from my own experience is my generator was running hot one day. My AC went to kick on, and the generator couldn't supply the required startup amperage, and so it bogged down the generator and the AC compressor. The AC tried to startup, and the generator engine tried to rev up to provide the power, but just couldn't make it. I hopped up like a jack rabbit and cut the AC off as fast as I could to limit damage from an undervolt condition.

This was from a generator that was WELL more than big enough to run my entire trailer in normal circumstances. But since it was borderline overheating, when the AC kicked on, it couldn't supply the required juice. Shore power would not have that problem.

I'm thinking there's something wrong with the generator in this case. Could be as simple as not enough ventilation (which is a common problem), a gummed up carb, a faulty/failing fuel pump, a clogged fuel filter... Or worst case scenario, something in the windings or stator inside the generator...

I'll be interested to read what OP discovers.