Generator A/C question

[Amg]

Something strange is happening with A/C. I turn on my generator (control located above front cabinet). I then walk to the rear on turn on the A/C. The unit will come on. I know I have to wait for the generator to be ready to turn on the compressor. It normally takes a few minutes. Lately the compressor never comes on. I notice all the lights on the generator are lit showing the A/C is being powered. However if I then turn the A/C off and then on the unit will cycle properly with the compressor. I keep a dog in the van and am concerned that the compressor will not turn on properly. Is something wrong or am I doing something wrong? Thanks

[InterBlog]

We, too, have a dog, and that would certainly make me concerned. I assume you're under warranty and that would be the way I'd go with the issue. However, if you want to first investigate further, here's a suggestion, for what little it might be worth.

Our Interstate is older, but it reportedly contains a buried switch that will keep the compressor turned off if someone attempts to use an appliance such as the microwave. So if I'm running a/c on generator and I want to warm up a burrito, the compressor should automatically shut off for the 2 minutes that I want to run the microwave, in order to free up enough power to run the microwave. I shouldn't have to go manually turn off the a/c for those two minutes, turn the microwave on, turn the microwave off, then turn the a/c back on.

However in our 2007, for whatever reason this feature doesn't work - we tested it two days ago when we were exercising the generator. There is no functional switch-over.

I don't know if your new model includes a similar control logic, but you might want to jack around with it and see if there are any usage sequences that produce identifiable patterns, and if such occurs, it might indicate a specific logic failure (with the caveat that, sometimes logic failures produce apparently spurious results that may not seem directly related to what's happening, like a PC spitting out the wrong error message because it doesn't have an error message specific to the actual fault).

For instance does your compressor failure to initiate happen every time regardless of circumstances or is there any association with having recently used generator power for other reasons? If you could identify patterns, it might help to fast-track any warranty work that you need to have done.

There's a good chance that some of the newer owners will comment more specifically to your model year and moot what I've said here, and that's OK.

[Boxster1971]

The late model Interstate's use a 120VAC energy management system made by Precision Circuits Inc., the same company that makes the Battery Isolation Manager (BIM). Here is link to the wiring diagram for Airstreams.
http://www.precisioncircuitsinc.com/...irstream-B.pdf

Here is user manual that explains how it works.
http://www.precisioncircuitsinc.com/...irstream-C.pdf

This electronic device sheds the 120VAC loads to keep from tripping circuit breakers. It takes a few minutes to recover once the loads are below the 20 or 30 amp limits. When generator is running the 20 amp limit is used.

The generator can only power the AC, with no other significant loads. Not sure this is causing the problem, but worth checking. You can tell from the display panel if a load is being shed.


- - Mike
2013 Lounge EXT on 2012 Sprinter

[Amg]

Thanks

I am not using the microwave, water heater, etc. I have been doing a little experimenting. I don't have the problem of the compressor not coming on when I turn on the generator and wait for all the lights to come on showing the A/C, microwave, etc is available and then turn on the A/C. I don't understand why the compressor will not come on when I start the generator and then turn on the A/C before all the lights come on. In that instance when the lights do come on my compressor won't. I can't find anything in the manuals from Airstream, Onan or Dometic giving any directions on how to turn on the A/C with a generator and whether one should wait for the lights to come on first.

Perhaps someone on the forum knows. Thanks

[UKDUDE]

When starting up the generator, the Precision Circuits Energy Management System takes a few minutes to start up and check everything before the circuits are ready to use. At that point all the lights on the right of the panel light up. Before then, you cannot use any of the 120V system, and that includes the AC.
It ought to be explicit in the Airstream manual, but isn't.

[Amg]

Thanks UKDUDE

All the lights do come on and while the blower on the A/C will come on the compressor never does. I waited 30 minutes. but if I wait to all the lights come on and then turn the A/C on the compressor will come on

[InterBlog]

Originally Posted by UKDUDE

...
It ought to be explicit in the Airstream manual, but isn't.

You're right, which immediately made me wonder where and how I'd learned it. Because learn it I did.

OP, you know the expression, "If Mama ain't happy, ain't nobody happy"? My Interstate analog is, "If Microwave ain't happy, ain't nobody happy". That's my mnemonic for remembering not to flip any other switches until I see that "0" light up on the microwave, which indicates that the system has completed its power-up sequence.

I've never tempted fate and flipped any "on" switch prior to seeing that "0". Interstates can be twitchy, and my view is, why risk it?

You may have just answered the question as to what kind of outcome can result if one risks it.

[73shark]

I've never tried to leave the A/C on and then start the generator but will bet that it won't come on w/o shutting off and then back on again.

Amg: Did yours ever work that way before?

[Amg]

Originally Posted by 73shark

I've never tried to leave the A/C on and then start the generator but will bet that it won't come on w/o shutting off and then back on again.

Amg: Did yours ever work that way before?

Yes. I first turned on the generator and then turned on the A/C. When the ready lights turned on the generator the A/C would come on and a minute later the compressor would come on.

[Boxster1971]

Originally Posted by Amg

Thanks

.... I don't have the problem of the compressor not coming on when I turn on the generator and wait for all the lights to come on showing the A/C, microwave, etc is available and then turn on the A/C. I don't understand why the compressor will not come on when I start the generator and then turn on the A/C before all the lights come on. In that instance when the lights do come on my compressor won't. I can't find anything in the manuals from Airstream, Onan or Dometic giving any directions on how to turn on the A/C with a generator and whether one should wait for the lights to come on first.

Perhaps someone on the forum knows. Thanks

I have not experienced the symptoms you describe because I always wait to apply loads to the generator until all lights on the Power Control System (PCS) display are on. I've looked through the manuals and you are correct there is no mention of a proper startup of the AC using generator power. But there are some hints.

1. The various Onan manuals I've looked at hint that there are some basic checks the generator goes through before it will provide full power. Proper oil pressure is one item. But I cant find anything more specific for the Onan Genset in our Interstates.

2. The Dometic Comfort Control Center 2 Thermostat in our Interstates has built in load shed logic that is connected to the PCS. I have observed that this is definitely a two stage load shed; one for compressor and one for the fan.

3. During start-up the air conditioner can draw more than the typical power needed to run. Too much load at startup can prevent air conditioner compressor from starting due to load shed by PCS.

4. You may not realize it but there is a load on the generator right after start that you can't control. It is the battery charger in the Magnum Inverter/Charger. It is a 50 Amp battery charger. Starting the generator draws a lot of current from the battery and the first thing that happens after a start is the battery charger replaces the power from the battery. This could easily be 5 Amps, enough to put the AC into a load shed mode. By waiting until all the lights on the PCS are on the battery charger is drawing very little, like 1-2 Amps or less.

Download this Onan RV Generator Manual for some basic ideas on how all this stuff interacts.
http://power.cummins.com/sites/defau.../F-1123-EN.pdf

Hope this helps,
- - Mike

[Amg]

Mike
Thanks a lot for the info. I will only turn on the A/C after all lights come on in the generator panel. I am going to closely monitor the situation to make sure the compressor does come on. I do keep a pet in the Van. Although I also have a temperature alert that will text message me if the temperature exceeds 75 degrees or if power is lost, I don't want only rely solely on an alarm. Thanks again

[bsedor]

Originally Posted by Amg

Mike
Thanks a lot for the info. I will only turn on the A/C after all lights come on in the generator panel. I am going to closely monitor the situation to make sure the compressor does come on. I do keep a pet in the Van. Although I also have a temperature alert that will text message me if the temperature exceeds 75 degrees or if power is lost, I don't want only rely solely on an alarm. Thanks again

Can you tell me what the temperature alert system is that you are using? I am researching that now.

Thanks.

Bob

[Amg]

It is a small device powered by AC or battery that will notify you by phone, email and text message if the the alarm is triggered. The temperature either low or high can be set and so can it if it loses A/C power or the battery is low. It just plugs in. there is a monthly subscription. There is an app for a smartphone where I can monitor everything remotely.

[73shark]

Originally Posted by Amg

I also have a temperature alert that will text message me if the temperature exceeds 75 degrees or if power is lost, I don't want only rely solely on an alarm. Thanks again

If the outside ambient is above about 85*, I doubt your rear A/C will maintain 75* by itself.

[Amg]

I live in south Florida. I lower the sun shades, cover the front window and side windows from the inside. Set the thermostat to 75 degrees. I frequently check the inside temperature remotely with my temperature alert and it does fluctuate between 75 and 77 degrees as the compressor cycles. Never had a problem in keeping the rear of the van 75. The front driving area is warmer as I would expect.

[Protagonist]

Originally Posted by 73shark

If the outside ambient is above about 85*, I doubt your rear A/C will maintain 75* by itself.

An air conditioner should maintain a temperature differential of more than the 10° you cite, unless it's either malfunctioning or woefully undersized. An Interstate's A/C is not undersized.

Under ideal conditions, my Interstate's air conditioner can maintain a differential of more than 30°F below the outdoor temperature. Under less-than-ideal conditions (parked in direct sun and facing a direction where the awning doesn't provide afternoon shade) it will still maintain a differential of at least 20°F below the outside temperature as long as I keep the windshield and windows covered.

The only part of an Airstream Interstate that is really well-insulated is the floor. So the more shade you have, the better. And the more you can block sunlight and heat from entering through the windshield and windows, the better as well.

[73shark]

Dometic says the drop across the evaporator is about 20* so everyone else's A/C must be operating a whole lot better than mine because w/ seven or eight people, it is lucky to maintain 85* and that's w/ the front running Max/Recirc.

[Protagonist]

Originally Posted by 73shark

Dometic says the drop across the evaporator is about 20* so everyone else's A/C must be operating a whole lot better than mine because w/ seven or eight people, it is lucky to maintain 85* and that's w/ the front running Max/Recirc.

Well, seven or eight people crank out a lot of body heat that I don't have to deal with as a solo traveler. Maybe that's the difference.

[bsedor]

Originally Posted by Amg

It is a small device powered by AC or battery that will notify you by phone, email and text message if the the alarm is triggered. The temperature either low or high can be set and so can it if it loses A/C power or the battery is low. It just plugs in. there is a monthly subscription. There is an app for a smartphone where I can monitor everything remotely.

Can you tell me who manufactures the device?

Thanks

Bob

[Amg]

Yes temperature alert. Their website is www.temperaturealert.com