Air Conditioner bogs down when running off Generator.

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LarsMac

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Nov 15, 2015
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Colorado Plains
We have been hanging out at daughter's home for a few weeks.
Plugged in to 20 AMP circuit from their garage, and everything has been working well.
Yesterday, we had to move out of range of the power source we have been using due to construction activity.
I started the generator (Onan Genset), mostly as monthly run.
We were out in the sun and it started to warm up, so Started the AC.
The AC would pull the generator down to almost a stall, and the the AC would drop, The Generator would build back up, AC would kick on, again, and bog the generator down, again.

We have not seen this before. we have on occasion run the AC for hours feeding of the generator power. (in a lot warmer weather, as well)
turned off the AC and let the generator run for an hour. No issue, at all. Then tried the AC again. Same problem.

We are back on shore power again, and AC is fine. (Still only 20 AM feed. )
Not even where to start to figure this out.
We plan to hit the road again by end of week, hope to have this resolved before we head out.
Any suggestions would be welcome.


 

HueyPilotVN

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Jun 5, 2012
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Lake Havasu City, AZ
Maybe the batteries were low and the combination of convertor charging and AC was too much until the batteries went off bulk.

Try shutting off the convertor temporary and see how the generator runs the AC.
 

Henry J Fate

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Run the AC off the genset without any other appliance running. Turn off all the 120 volt breakers except for the air conditioning. See if that works.

There could be multiple problems contributing to the start up failure. The air conditioning can draw over 20 amps when starting up and will settle in to a much lower amp draw once running.

The genset may need service. Air cleaner, spark plug, oil change, rpm adjustment etc.

The ac could also be drawing a higher than normal start up amp draw.

Posting your specific genset and ac model will help in getting better info.
 

Isaac-1

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SW Louisiana
It could be either the air conditioner has a high initial start up draw, possibly due to a capacitor that is going bad, or it could be that the generator is having issues supplying its rated output power.  Without test equipment it really is hard to say which one it is.    A simple test would be to turn off everything else that the generator powers in the RV (refrigerator, converter, water heater (if electric), etc.) and plug in some test loads (into outlets on different breakers so you don't trip a breaker in the panel) of roughly known power consumption, cube heaters, and hair dryers work as an example and see if running these bogs the generator down.  Hair dryers are typically 1,500 watts on high, and 750 watts on low, so 2 hair dryers on hi and 1 on low will be about 3,750 watts, which is close to the output rating of a typical 4,000 watt Onan generator.

If the generator bogs down and stalls with the hair dryers, then it needs a tune up
 

xrated

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"Murvil", E. TN.
Isaac-1 said:
It could be either the air conditioner has a high initial start up draw, possibly due to a capacitor that is going bad, or it could be that the generator is having issues supplying its rated output power.  Without test equipment it really is hard to say which one it is.    A simple test would be to turn off everything else that the generator powers in the RV (refrigerator, converter, water heater (if electric), etc.) and plug in some test loads (into outlets on different breakers so you don't trip a breaker in the panel) of roughly known power consumption, cube heaters, and hair dryers work as an example and see if running these bogs the generator down.  Hair dryers are typically 1,500 watts on high, and 750 watts on low, so 2 hair dryers on hi and 1 on low will be about 3,750 watts, which is close to the output rating of a typical 4,000 watt Onan generator.

If the generator bogs down and stalls with the hair dryers, then it needs a tune up

Great answer Isaac.....you nailed it.
 

LarsMac

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Colorado Plains
Thanks for the replies.

The A/c works fine off the house 110v 20A feed. 
The generator has clocked 146 hours now. last maintenance was at 98, just before we started this trip. oil looks good, and air filter, as well.
I will look at the wiring and Spark plug during the day, tomorrow.
There is a Cummins service over near Portland, I may try to get it in for an officlal 150 hr maintenance this week.
 

Henry J Fate

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Try turning off all the 110 volt breakers except for the ac breaker then fire up the ac off the generator. That could turn out to be valuable info
 

LarsMac

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Colorado Plains
So, had a chance to work on this today.

1. Oil level on the gennie (Onan 4K) was approaching the fill mark. added .7 qt close to full now.
2. Air filter is clean.
3. Checked Spark plug. Looked good, except for some black residue. Gap is at .25 as recommended. Looks like the fuel mix is a tad rich. Cleaned and re-inserted.
4. There is an air/fuel adjustment for choosing operating altitude. 
from the manual, there should be a pointer to indicate altitude setting. No such pointer exists.
so, Since I cannot be certain what the fuel mix actually is, I started with a couple of assumptions. Since the last maintenance (well all maintenance, since the thing has always been in Colorado) in the Denver area, I presume that the setting was originally at 5000 feet. We've been running around sea level for the last two months. The rich mixture might be due to that setting still being for 5k ft.
I turned the setting a bit to the left,
Started it up. It would seem that I turn the mix a bit too far. much sputtering and choking.
So, adjusted the fuel mix back to the right, and engine started smoothing out. found a spot where it runs well, and good RPM.
Launched the A/C
genny still running smooth, A/C working well. Started the Microwave up. barely a shift in the RPM.
I think we are good to go. For now.
Will hunt down a Service site somewhere between here and Chicago, to see about making sure it is optimal. 

 

Henry J Fate

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That's good news. Those pointers are known to break off the carb. When I purchased my unit, I found the pointer in one of the kitchen draws. Didn't know what is was until I did a complete service on the microquiet 4000. I had to estimate the setting by looking at the broken stem and aligning it up. Another way to check for a proper setting is running the genset under average load and then pulling the plug and looking at the electrode. Should be a nice tan and dry looking electrode.
 
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