Front AC Compressor not working when Genny and Engine Running together

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The Reilly's

Active member
Feb 22, 2013
Myrtle Beach, SC
Newbie here....We have a 2004 Fleetwood Bounder, Onan 5.5 Generator.  Both the front and rear A/C's works perfect on Shore Power, shedding like they should.  They both work perfect on the Genny (they run concurrently).  However, I want to run them while driving and now find that when the Engine and Genny run together, only the rear A/C (2) works.  I've tried both separately, and as soon as I turn on the front A/C with Engine and Genny running, it goes right to the red shed light (red light is steady, "NO GREEN LIGHT AT ALL") and only the fan works, not the compressor. I've reset all the breakers in the coach and on the Genny itself and now I'm puzzled ????? 
I'm puzzled too - can't conceive of any correlation there. About the only connection I can think of is that the Energy Management System is 12v powered and maybe it is going haywire when the 12v is coming from the engine alternator. But that's a real stretch...

I'm guessing from your description that the Bounder has a 30A shore power system. That means the rear a/c is wired for direct operation from the generator but shared main (30A) power when using the shore cord. So the rear a/c is running through different wiring when on generator power. I'm wondering if you have tried other main power items with generator and engine on? Microwave, fridge in AC mode, etc. Do those work ok or do they shed too? 
Yes - it is a 30AMP Service.  I will definitely try running the Microwave or W/D tomorrow with the Genny AND Engine running and see if I have same problem.  Thanks - I will let you know !! (PS:  Sorry for posting same in two area's - I know that is wrong but when I didn't see any replies at all, I thought I posted it under the wrong area and didn't know how to delete the other posting).
Okay Gary, just got back from RV  :( . Ran Genny, Ran Engine, everything else off, Microwave ran fine.  Washer ran fine.  Turned on back A/C and it ran fine, turned it off, waited, then turned on Front A/C and it went right to steady red shed light mode LOL.  Decided to try something else that I saw when googling problem since I know it worked once for me, then last 2 times it didn't.  I have been starting Genny, waiting few minutes, then turning on A/C, THEN starting Engine later when ready to go.  This time, I started Engine 1st, then Genny, waited few minutes and when I turned on front A/C, instead of it going right to steady red shed mode, it flashed red and green back and forth like it was trying.  I got excited, but it kept flashing (although I only waited few minutes ... maybe I should have waited longer but the back comes on soon after the flashing back and forth). So..back to square one!  Another thought - someone had installed an inverter after the fact.  It has an extension cord plugged into one of the two outlets and I traced it to the back where the shore power cord is stored.  Seems like it's just there to maybe plug something into if needed since it doesn't work anything in the coach when on.  So..... I thought that I would have my husband disconnect the inverter from the battery tomorrow and see if that does anything in case they installed it incorrectly.  Just a thought - I'm clueless but "process of elimination" before $$$$$ into service  :'(
My coach has a 50 amp generator, but only 30 amp service. Only has 1 airconditioner, but is wired for 2. Instructions in the owners manual states I can only run one air on shore power but both on generator power. There is some switches located near the power center that have to be flipped a certain way to run either front air or rear air. Maybe yours have the switchs also. I only have a 30 ft coach so no need for the 2nd air. Is your generator a 50 or 30 amp?
Thanks 92GA !!  This is correct.  On Shore Power (I am 30 amps) you can only run one at a time.  My coach has the Intellitec ECM so it bounces back and forth automatically which is nice.  Each A/C is wired to a separate 20 amp breaker, therefore, when hooked up to Shore Power, it can only handle one at a time (about 13 amps each at a time).  My Generator is 5.5W which gives me 45 amps and since each A/C is wired to a separate breaker, they can both run at the same time.  They both work fine and work like above, my problem is that as soon as I start the Engine (I want to have the front Roof A/C going when I travel because the Dash doesn't do enough) the compressor for the Front one shuts down and only the fan runs.  The Back Roof A/C works while driving though but it's too far back and I'd rather use the Front one.
Don't waste time disconnecting the inverter - it is not involved in any way unless you plug the shore cord into that extension.

You should start another discussion to talk about how to employ your add-on inverter - I don't want to confuse this one with a second and unrelated question.
Thanks for checking the other 120v appliances - that narrows things down a bit.

Forgive me, but one more question to make sure we understand the issue exactly right: With the engine off, you can start and run the generator and both a/c's will run. Is that correct? There should be no load shedding in that scenario, cause the rear a/c should be running direct from the generator on its own circuit, while the front a/c draws power from the 30A main supply, which also comes from the generator.  Then, after both a/c's are running, if you start the engine and quickly the front a/c shuts off and the load shed light comes on?

I'm struggling to find any connection between the main engine and the rooftop a/c. Starting the engine introduces an additional source of 12vdc power, but nothing that affects the 120vac power for the a/c. The only thing I can come up with is the 12v power used by the EMS itself.  Let's try resetting the EMS, which is done by removing its 12v power. The easiest way to do this is to turn off your battery disconnect switches, both main and auxiliary, for about 15 seconds, then turn back on. See if that has any effect. It's a long shot, but worth a try.
Yes, both A/C's work fine on Shore Power alone and with Genny running. Back A/C runs fine with Genny AND Engine running. It's just the front A/C. The fan runs, but red shed light stays steady and no compressor  with Engine running. Of course I wait few minutes after Engine and Genny run before turning on Air and it goes right to red shed light but only in this scenario.

I assume you mean turning off the two battery disconnect switches (Aux and Main) with everything OFF???  If so, we disconnect batteries as soon as we are done and leave camper as a rule. Or do you mean disconnect them with Engine and Genny running to reset??? And while A/C power is on???
I'm reading back your reply again after posting and noticed something you said (sorry). I will try having genny running, both A/C's running for a bit normal, THEN start engine.  I will then see what happens and how long it takes to affect front A/C.  Right now I've been testing it by turning A/C on after both are running.  Will let you know. We are taking out for few days today :)
I assume you mean turning off the two battery disconnect switches (Aux and Main) with everything OFF???

Right, no shore power, no generator, and no engine.  Removing 12v power forces the EMS to re-boot when power comes back on and sometimes it clears a fault in its controller. This is a real shot in the dark, but easy to do.
Sorry to ask you to keep clarifying and re-testing, but this is a very, very strange problem. There are so few possible points of interaction with the engine running that I'm clutching at straws!

I just thought of  another experiment that may shed some light.  Instead of actually starting the engine, just turn the key to on and try the generator + front air combo.  I'm trying to ascertain whether it is the ignition being on that triggers the problem  or whether the engine has to be actually running to cause it. When the engine runs the alternator begins supplying 12v power throughout the coach, but with just the key on, it does not.

Also, does your coach have a switch anywhere that shifts the rear a/c from shore power to generator, or otherwise affects how the rear a/c receives power? Cause something has to tell the RV electrical system that the generator is on and to shift the rear a/c to the secondary generator output circuit.
The EMS is rebooted each time then because we always disconnect the batteries (Aux and Main Chassis) with the switches whenever we leave the camper at the end of our trip.

I will definitely also try what you said today, just turning the key to accessory without actually starting the engine and let you know!

As for switching the rear A/C from Shore to Generator power, there's no switch that I know of that's accessible, I thought that was was the "Transfer Relay Delay" box does besides switch from front to back automatically?
Okay.....Genny running, Front AC going fine, compressor on. Turned key to accessory, nothing happened.  Started engine, compressor went off in seconds, green light off, steady red light (fan still runs though).

Decided to try something else. With engine and genny running and A/C with red light on steady like above, started flipping breakers on and off and watching lights. When I flip the 20 amp breaker that is marked Converter/App, the ECC light goes from red to green for a second then back to red. It is the only breaker that seems to have some effect.  Does that tell you anything?

It suggests that there is a major power draw from the converter (and/or whatever else shares that circuit), but it should be no different with the engine running than at other times.

You said "Turned key to accessory". Did you mean the actual Accessory position, or the On position? They are different in that additional circuits are activated in "ON" vs "ACC". Typically, ACC is a short turn to the left and ON is a short turn to the right, prior to the START (engine cranking) position. Sorry to nitpick, but details are crucial when troubleshooting.
Gary, am puzzled also but I am going to tell you about my experience with an older 30amp Damon coach.  Normal Connection for the BR A/C (2) was:

1. On SP the BR A/C received its power from EMS thru the Transfer Switch and would work on 30amp depending on what other AC loads being controlled by the EMS were doing.  The 20amp was part of the MH's CB Panel.  It would even let both A/C fans  run simultaneously but usually only one compressor, most people thought both A/Cs were running.

On Genny power the BR A/C is direct wired to the Genny thru Transfer Switch and uses the 20amp CB on the Genny.  The other leg of the Genny feed the remainder of the Coach.

That being said it certainly points to the EMS and the 12v power it is receiving, I would start by disconnecting the current 12vdc input power from the EMC and connecting the EMC to a standalone 12vdc battery to isolate the EMC from the Alternator and, if possible, wrap the EMS with Aluminum foil. 

I would then start the engine and see if you get the same results.  If you don't and everything is working correctly, first remove the Foil to see if it is interference from the engines electrical system.  If removing the foil makes no difference and everything is still running correctly  that tells you it is interference from the alternator, I would measure the AC content of the output of the Alternator.

Walt's explanation is typical of a 30A coach with an EMS and pretty much how Fleetwood has always done it. I have no direct experience with a 2004 Bounder, but am fairly confident it works the same way.

So it appears here that the problem begins when the engine alternator comes online and starts providing 12v power. It must be backfeeding into some 12v circuit and disrupting it, and ultimately fooling the EMS into shedding some loads. Strange that it is just the front a/c that is shed, though.  I am dubious that we can diagnose any further from a distant keyboard. I think it is going to take a skilled tech with a meter to start checking what power is flowing and where.
I found and fixed the problem!!  I was driving hubby nuts trying to figure it out but I don't give up a challenge!  I learned everything aboard but there was one thing that kept bothering me which was the inverter I mentioned before. It was put in afterwards, was not hooked up to anything except a big extension cord that he ran to opposite side by the shore power cord. It was sloppily done too. Plus, I know it's just a drain to the battery when on. we were leaving yesterday, I decided to "eliminate" the thought and disconnected the inverter. I started the genny, started the engine, put on the back A/C all fine. Put on the front A/C and BINGO!  Both A/C's running, compressor on...drove all the way home in a wonderful 68 degree RV!!!  :)

Thanks for all your help!

There's only one more qquestion I have for's a switch I can't figure out but I'll start a new post and put a pic of it!

Donna....cooled off and HAPPY!

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