Help-AC/Gen issue

[Interstate65]

Just had the Onan service center install new 2500LP gen-everything works great except when the compressor kicks in- it will run for 10 seconds to 4-5 minutes then the compressor cycles off-fan on Ac still runs- plugged into shore power Ac runs fine. BTW-also I stalled new inverter at the same time-same as what was in it.
Thanks for any insight-can’t Get it into service at Airstream dealer until Sept 16!!

[amirm]

It sounds like there is not enough power to run the compressor. Try it when it is cooler. I bet it will continuously then.

[Lily&Me]

Perhaps try the Onan service center?

Seems the issue is with the generator...

Maggie

[Boxster1971]

Originally Posted by Interstate65

Just had the Onan service center install new 2500LP gen-everything works great except when the compressor kicks in- it will run for 10 seconds to 4-5 minutes then the compressor cycles off-fan on Ac still runs- plugged into shore power Ac runs fine. BTW-also I stalled new inverter at the same time-same as what was in it.
Thanks for any insight-can’t Get it into service at Airstream dealer until Sept 16!!

Your problem is likely NOT the Generator or the A/C. If it is like mine it is the Airstream installed EMS that controls the 120VAC loads. Here are several recent post on the topic. The fix is very simple. Just switch off the Microwave and Receptacles 120VAC circuit breakers to disable the EMS. You then have to manage other loads manually as the generator can power little more that the A/C.

http://www.airforums.com/forums/f240...ml#post2017779

http://www.airforums.com/forums/f240...ml#post2106640

[OTRA15]

Did you call the place that just installed it? Presumably they test ran it for a while after installation!

[Alex AVI]

Originally Posted by Interstate65

Just had the Onan service center install new 2500LP gen-everything works great except when the compressor kicks in- it will run for 10 seconds to 4-5 minutes then the compressor cycles off-fan on Ac still runs- plugged into shore power Ac runs fine. BTW-also I stalled new inverter at the same time-same as what was in it.
Thanks for any insight-can’t Get it into service at Airstream dealer until Sept 16!!

INTERSTATE65 - my unit uses same 2500LP. That generator runs my A/C with no problem even at 115°F or at 8,500 ft. asl. Howevr, that's all it will run. If you try to run/use the microwave, or any other loads which combine to push it's already teeny margin past threshold, it will SHED the A/C as it is the 1st item in the EMS SHED list. So as MIKE said, either switch off the microwave ckt brkr (coz that disables the EMS also) or just turn off every light, fan, appliance when A/C compressor is on AND especially if it is on HIGH. What I have noticed is when the A/C is on LOW, even if compressor is running, I can leave the microwave powered (but definitely not being used) without the EMS shedding the A/C. There is no problem, other than it's just capacity limitations. Most of us have learned to manage loads manually before the EMS does the managing for us. Best of luck on usage of new gen.

[gmillerok1]

This doesn't make sense to me. If the setup is the same as mine, and the genset can't produce enough amps for the AC, would it not stall, not simply turn off the compressor while leaving the fan on, even if the EMS was shedding loads?

Does the same behavior occur on shore power or does this only occur with the genset?

I note that the genset is notrecommended by Dometic for a 13,500 btu ac unit, as the unit when starting up uses more amps than the genset can continuously generate at startup because of the surge, but I think it should stall, rather than simply turn off the AC compressor.

I cannot understand how only the AC compressor would be effected if the genset couldn't handle the load, particularly after it has started up for awhile.

[Boxster1971]

Originally Posted by gmillerok1

This doesn't make sense to me. If the setup is the same as mine, and the genset can't produce enough amps for the AC, would it not stall, not simply turn off the compressor while leaving the fan on, even if the EMS was shedding loads?

Does the same behavior occur on shore power or does this only occur with the genset?

I note that the genset is notrecommended by Dometic for a 13,500 btu ac unit, as the unit when starting up uses more amps than the genset can continuously generate at startup because of the surge, but I think it should stall, rather than simply turn off the AC compressor.

I cannot understand how only the AC compressor would be effected if the genset couldn't handle the load, particularly after it has started up for awhile.

The problem only occurs with generator on my 2013 Interstate. The generator uses a different EMS setting than on shore power. I researched this at vendors web site some time ago and the lower limit can be only 18A, but is adjustable by factory. I think this is my problem since I can run the A/C off the generator all day long if I disable the EMS from controlling the load. It also runs fine on shore power with EMS set to 20A. There are different models of the Precision Circuits Inc. EMS units used by Airstream. Thus the problem might not effect everyone. I'm attaching the files of what I found and the comment that:
"Mini-PCS max current level range is 18-90 amps and set at Precision Circuits"

Some later models may have the GEN limits at 20 or 22A, but I have observed mine trip at 18A many times. The work around is no big deal since you CANNOT run anything else is you are running A/C on generator.

[Alex AVI]

Originally Posted by gmillerok1

This doesn't make sense to me. If the setup is the same as mine, and the genset can't produce enough amps for the AC, would it not stall, not simply turn off the compressor while leaving the fan on, even if the EMS was shedding loads?

Does the same behavior occur on shore power or does this only occur with the genset?

I note that the genset is notrecommended by Dometic for a 13,500 btu ac unit, as the unit when starting up uses more amps than the genset can continuously generate at startup because of the surge, but I think it should stall, rather than simply turn off the AC compressor.

I cannot understand how only the AC compressor would be effected if the genset couldn't handle the load, particularly after it has started up for awhile.

GMILLEROK1 - after re-reading OP, you make a valid point. I think I read OP description incorrectly, this part:
"the compressor cycles off-fan on Ac still runs- plugged into shore power Ac runs fine"

The way I understood above was :
"the compressor cycles off fan on Ac" -and- "still runs plugged into shore power Ac runs fine"

In retrospect, you are absolutely right. If EMS did shed A/C, compressor & fan would both not run. I have seen that happen on mine when I am plugged into 20A shorse & EMS is set to 20A and I forget to turn off stuff during A/C startup . Maybe OP can clarify behaviour?

[Boxster1971]

I just ran a test on mine. When the EMS drops the load about 10 seconds after the A/C compressor starts the compressor stops, but fan keeps running for a few more seconds until the EMS shuts down everything. Can’t tell for sure if this is the OPs issue from the minimal details. I’ll wait to hear more. All I know is on mine if I turn off the GFI Receptacle breaker it shuts off the EMS and then the A/C works fine on generator power. Don’t need to do this work around on shore power.

[Alex AVI]

Originally Posted by Boxster1971

Can’t tell for sure if this is the OPs issue from the minimal details. I’ll wait to hear more.

MIKE - I agree. There's something not reconciling with OP description also. Coz on Jul 5, OP had posted on new thread:

"Issue: 13,500 BTU A/C- kills the generator when the compressor kicks on,
possible causes?"

Advice was given my RMKRUM but there was no acknowledgement from OP as to outcome. And then to jump from there to replacing the gen seems like a very drastic step. I kinda wish folks who ask for help close the loop with the good folks here who try to help and/or give advice. If that was done on OP's 1st cry for help, we might be in a much better place today with regards to continuity and maybe even prevent an unnecessary gen purchase?

[rmkrum]

What's that old saying?

"You can lead a horse to water, but if you get him to do the backstroke, you've really got something..."

Or something like that.

Lack of acknowledgement is not unusual, people get busy. But, as a group, we freely keep handing out advice anyway.

I've received some really nice PMs from folks that I have somehow managed to help. Makes it worth it, IMHO.

[Alex AVI]

Originally Posted by rmkrum

"You can lead a horse to water, but if you get him to do the backstroke, you've really got something..."

I've received some really nice PMs from folks that I have somehow managed to help. Makes it worth it, IMHO.

RMKRUM - Never heard it put that way. And yeah, those nice PM's make it worth it.

[rmkrum]

Too much snarky at times. Or too much Mad Magazine, maybe.

Yup, the occasional “Thank you” note restores my enthusiasm to write lengthy but accurate as I can make them type answers.

[OTRA15]

Originally Posted by Interstate65

. . .
Thanks for any insight . . .
. . .

Wondering if you got this sorted out?

Thanks,

Peter

[Interstate65]

Thanks for all the good info-turned off the inverter and the breaker to the micro-wave-AC works perfectly-I wonder if there is a way to fix this issue-since a larger generator won’t fit under the Interstate

[Alex AVI]

Originally Posted by Interstate65

Thanks for all the good info-turned off the inverter and the breaker to the micro-wave-AC works perfectly-I wonder if there is a way to fix this issue-since a larger generator won’t fit under the Interstate

INTERSTATE65 - Easy, buy a Soft Start for your Dometic and/or get rid of your Precision Control Systems EMS Mini and replace with the MIDI version. My 2018 has same 2500LP gen, NO gen auto/softstart, and PCS EMS MIDI and I have no issues holding A/C (alone) at 115°F or 8,500 ft. ASL unless my old brain gets stupid/forget and adds more load.


From MIDI Spec sheet:
"Midi-PCS senses the Generator Hour Meter signal to know the Generator is running.
When the generator first starts, Midi-PCS performs a soft start, shedding all the
appliances, and turning them back on one at a time, after a 2-minite delay. The Midi-PCS
operates the same as above (Mini), except the current limit is adjusted to match the size of Generator."

Or as MIKE has suggested and you confirmed it works, do it the manual way he does. Works just as well! Take your pick, the first 2 options cost money and the 3rd option is FREE!

[Alex AVI]

UPDATE -
MIKE , GMILLEROK1, RMKRUM, INTERSTATE65

On units using the PCS MINI, the shed relay is ONLY for the A/C compressor. This solves the mystery of why compressor sheds while fan stays running awhile.
MINI 600 - shed relay 3 compressor only
MINI 610 - shed relay 4 compressor only
MINI 611 - shed relay 3 compressor only

On PCS MIDI (mine) per install spec sheet for Airstream Interstate :
02-10-2018 - shed relay 2 is fan, shed relay 3 is compressor (I assume prior dates inclusive)
02-12-2018 - shed relay 3 is compressor (I assume later dates inclusive)

Dates are per PCS, not AS build dates.

So as you can see, there's many multitudes of combo shed hierarchy that has been implemented by PCS & AS along the way, making us all constantly guess WTF is this not making sense?

[rmkrum]

Makes sense, in a nonsensical way...[emoji3]

[Boxster1971]

Alex - great info. Thanks for the details. Also glad to know Airstream is using the improved MIDI now.