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Old 02-20-2019, 02:21 PM   #1
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2 AC Units - Program thermostat to run both at same time?

I have 2 factory installed ac units in my 2017 flying cloud. The thermostat has me setting zone 1 and zone 2 separately. Which means that one ac unit is generally running to cool both zones. The second unit never turns on because the interior is cooled by the first unit.

I’ve tried setting each zone at different temperatures but the end result is that one ac unit does all the work while the other ac unit sits idle.

Can I program the thermostat to run them both at the same time? Seems much more efficient to use them both instead of allowing only one unit to do all the work.
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Old 02-20-2019, 02:27 PM   #2
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They should definitely run at the same time if the demand call from the thermostat is there. At least that is the case for us, it usually only happens when we first hook up for the initial cool down. Then one unit mostly runs the show. We use the thermostat programming to run the unit in front at night and in the back during the day. 27FB
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Old 02-20-2019, 02:42 PM   #3
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Thanks. Yes, they both run at start up. But like you, one ac unit will take over and run to cool both zones, while the other unit sits idle. I’d prefer that both ac units run at the same time to cool our airstream. Seems much more efficient than having one ac unit do all the work while the other ac unit sits idle.
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Old 02-20-2019, 03:48 PM   #4
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One unit is running because that's all that's required.
I sometimes will turn off the front unit, or run on "fan only" to minimize the noise if I'm in the front.
Same theory in the bedroom, run the front unit and the noise in the bedroom is reduced.
Two units are very powerful, consider it efficient.
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Old 02-21-2019, 11:21 AM   #5
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Quote:
Originally Posted by Richz3 View Post
I have 2 factory installed ac units in my 2017 flying cloud. The thermostat has me setting zone 1 and zone 2 separately. Which means that one ac unit is generally running to cool both zones. The second unit never turns on because the interior is cooled by the first unit.

I’ve tried setting each zone at different temperatures but the end result is that one ac unit does all the work while the other ac unit sits idle.

Can I program the thermostat to run them both at the same time? Seems much more efficient to use them both instead of allowing only one unit to do all the work.

In order for the two low voltage power supplies to remain isolated, it is necessary to incorporate a master/slave control between the two units and one of the thermostats, whereby one thermostat controls two relays controlling each of the cooling functions, two for controlling the two heating functions, and for controlling the two for the fan functions. This puts a single thermostat in control of the two independent units.

Sounds complicated but in practice it is relative easy. You might take a look on Amazon … ebay … utube for such a ready made solution. If you don't find anything, I can help you with the details and final product and installation. Good Luck.
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Old 02-21-2019, 12:49 PM   #6
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Just set the temp to 40 degrees for
Both and they’ll both run non stop
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Old 02-21-2019, 03:31 PM   #7
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In order for the two low voltage power supplies to remain isolated, it is necessary to incorporate a master/slave control between the two units and one of the thermostats, whereby one thermostat controls two relays controlling each of the cooling functions, two for controlling the two heating functions, and for controlling the two for the fan functions. This puts a single thermostat in control of the two independent units.



Sounds complicated but in practice it is relative easy. You might take a look on Amazon … ebay … utube for such a ready made solution. If you don't find anything, I can help you with the details and final product and installation. Good Luck.


Sounds like the solution I was after - thanks. I’ll check it out and get back to you if I need any help.
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Old 02-21-2019, 10:11 PM   #8
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I don't believe running both at the same time would be anywhere near as efficient as just running 1 if the demand isn't really high enough for both. It would cause sort cycling which can reduce the useful life of the AC units. If there is high humidity they may not control it well and a lot of the efficiency would be lost trying to reduce the humidity.
The only real benefit of running both when 1 is enough is less time making noise.
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Old 02-22-2019, 04:59 AM   #9
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You may also want to consider times when less than 50 amp service is available to power both units.
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Old 02-22-2019, 07:02 AM   #10
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Richz3,
Your Dometic dual AC/Heat pump system using Dometic CCC2 TStat already has the feature built in!

There is no need to add any additional equipment, except one suggestion.

Down load the operations manual from the Dometic web site, (PDF) and look at page 16.

It will tell you how to set up “dual stage” operation where one compressor is primary and the other is slave.

In this way the entire vehicle is kept at your desired temperature and each is cycled as necessary .

Now the one “add on”.

If you don’t already have them, have installed MicroAir “Easy Start” units in both AC’s. Your AC/Heat pumps will love you and you will love them.

Safe Travels.
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Old 02-22-2019, 07:09 AM   #11
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Great post. Thanks to everyone for the quick replies!
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Old 02-22-2019, 07:21 AM   #12
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You are over-thinking this. The system will run both, if there is demand. Set the temp lower on the unit you want to run as primary. Then leave it alone. Adjust front/rear temps as required.
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Old 02-22-2019, 12:10 PM   #13
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What is all the fuss? Disconnect the remote sensor from the #2 air conditioner. You can find the connector above the air intake. All modes will default to the main sensor in the CCC2. Both ACs will cycle off and on at the same time within 10 sec. of each other, as will the heat pump operation.

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