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Old 08-30-2022, 10:07 AM   #1
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3rd AC

So I am wanting to add a 3rd AC to my 43 ft cardinal luxury model 3700 5th wheel trailer. It already has one in front and one in the rear. I Want to add one in the center of the coach in the kitchen area. My question is how do I find out where to cut a hole in the ceiling to install the unit and how to tie into the existing duct work in the trailer. There is a set of intake vents already in this area so Iím assuming you can add one here plus I have seen many other cardinal luxury models that have one in this location. But how to locate the ducting in the ceiling is another story. I donít want the unit to come through the ceiling and be seen at all. You canít see either one of my other units either. Nothing protrudes down through the ceiling. Plus how do I know if it is pre-wired for a third AC. Any help or advice would be greatly appreciated on this issue. The trailer stays down here on the Texas coast full time and does get quite hot. In the afternoon the existing AC unit can just barely keep the Rv in the mid 80ís, thatís too hot to stay in. And one of the existing units is brand new, just bought it last month. I currently have two low profile dometic penguin II 15k units and desperately want a third.
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Old 08-30-2022, 10:23 AM   #2
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following this one!
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Old 08-30-2022, 12:29 PM   #3
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??

I donít know what you mean !!
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Old 08-30-2022, 03:06 PM   #4
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Is there a vent in the middle area?
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Old 08-30-2022, 03:43 PM   #5
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Our cardinal is a different floor plan but it has a standard ceiling vent in the middle. I’m sure you could use the opening to mount an additional a/c. But what I don’t know about is how to tie into the ducts that are in the ceiling. You would probably have to run 120 volt power cables, install a thermostat, and run the thermostat wires. I’m just wondering how much of an effort all that would be.
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Old 08-31-2022, 08:03 AM   #6
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I'm not familiar with your unit, but generally an existing center vent is used, and there may be some pre-wiring at that location. I think you have to have the unit showing from the inside as it won't be tied into the ducting.
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Old 08-31-2022, 08:37 AM   #7
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your probably better off finding out why your existing 2 a/c are not keeping up



a) they are dirty and need a good clean ?
b) air leaks in the a/c unit or ducts
c) check if a/c is freezing up
d) park trailer where more shade
e) sunblock on windows by either some film, insulated material , Heavy curtains
f) slide toppers .... slide roofs / walls are sometimes poorly insulated
g) air leaks in doors etc
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Old 08-31-2022, 02:28 PM   #8
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My rig does have a power vent in the kitchen area but it is skewed off to one side over where the stove is, it is not in the center of the celing. Managed to get a hold of forest river and they stated my rig is set up and pre wired for the third AC. They are going to email me blueprints of the ceiling structure based on my vin number. Don’t want the unit to protrude into the celing at all, that is a deal breaker. Thanks for everyone comments. Still have to figure out tie in to the ducts
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Old 08-31-2022, 04:32 PM   #9
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So if you use the existing vent hole and tie into the existing duct work and have nothing protruding down from the ceiling, how are you going to cover the vent hole in the ceiling?
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Old 08-31-2022, 04:33 PM   #10
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I was under the impression that the ducts are shared by the A/C's. So if you cut in line with your other two you are going to "hit" the main duct line.
I have two A/C's and when either is running without the other, I get air coming out of the vents. It is weak, for example: If the rear A/C is on you can feel air coming out of the bedroom duct. Not a full blast like the duct in the rear, but air is still coming out.
And vice versa: If the front bedroom A/C is on air comes out of the vents in the kitchen. Again, a weaker stream, but it is there.
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Old 08-31-2022, 04:41 PM   #11
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Originally Posted by CHICKDOE View Post
So if you use the existing vent hole and tie into the existing duct work and have nothing protruding down from the ceiling, how are you going to cover the vent hole in the ceiling?
Darn good guestion. I would prefer a center dump and not try to find the existing ductwork. Youíll be lucky to find the romex and thermostat wire.
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Old 08-31-2022, 09:15 PM   #12
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So Iím not interested in using the vent hole for the AC. Like I said it is way over to one side of the trailer. And I believe you tie in to the ducts from the top side On the roof just like the ones that are currently on the rig, but am a bit concerned about cutting a hole in the roof material and not finding the ducts where they are supposed to be, then I have to put on a new roof membrane.
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Old 08-31-2022, 09:31 PM   #13
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I think I would be more concerned if the power is there in the ceiling.
Also putting the third thermostat in a location that would allow it to function properly.
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Old 08-31-2022, 10:18 PM   #14
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Sounds like a pretty big Jon to me. So leave the vent as is. Cut a new hole right in the center for the new a/c. You’ll have to run wires and frame that hole do it will hold the new a/c securely. You’ll need to cut from the new a/c over to the exiting ducts and fabricate connecting ducts. Then rebuild the roof.

Or pull the ceiling panel down from the inside and work from the bottom. You’ll still have to cut through the room and frame it. But you should be able to install the new ducts and recover them with the ceiling panel. I think I’d rather pull the inside ceiling panel than make large cuts in the roof.

Or, use the existing vent hole. Direct the air flow from it to compensate for it being off center.

You might want to check with a rv repair / service / modification center to see if they would even quote doing what you want to do. That may give you an idea of how hard it would be.
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Old 09-01-2022, 02:34 AM   #15
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I'm with Aussie, find out why 2nd isn't keeping up. Then i check with a professional see what their take on it would be. then proceed from there.
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Old 09-01-2022, 07:13 AM   #16
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I'm with Aussie, find out why 2nd isn't keeping up. Then i check with a professional see what their take on it would be. then proceed from there.
I have the same size Cardinal as OP's and I can tell you there have been times when my two A/C's don't completely keep up.
I am in NC and on the really hot and humid days they get pushed to the limits.

Why? pretty simple, lack of insulation in the build.
Come winter flip that to the opposite with heat.
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Old 09-01-2022, 07:19 AM   #17
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Sounds like a pretty big Jon to me. So leave the vent as is. Cut a new hole right in the center for the new a/c. Youíll have to run wires and frame that hole do it will hold the new a/c securely. Youíll need to cut from the new a/c over to the exiting ducts and fabricate connecting ducts. Then rebuild the roof.

Or pull the ceiling panel down from the inside and work from the bottom. Youíll still have to cut through the room and frame it. But you should be able to install the new ducts and recover them with the ceiling panel. I think Iíd rather pull the inside ceiling panel than make large cuts in the roof.

Or, use the existing vent hole. Direct the air flow from it to compensate for it being off center.

You might want to check with a rv repair / service / modification center to see if they would even quote doing what you want to do. That may give you an idea of how hard it would be.
If Forest River gets a set of roof prints to OP and they are claiming there is power in the roof for third A/C, then it really is not much of a job to add that third unit.
Maybe mis communication, but the A/C set up is completely ducted on these Cardinal's. There is no main frame that blows the air around from one point where the units drops in.
I am going with my earlier statement that there is most likely a main trunk running the length of the roof and the A/C's all get set up into that trunk.
Waiting for OP to get the info from Forest River.
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Old 09-01-2022, 07:44 AM   #18
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Originally Posted by kr1928 View Post
So Iím not interested in using the vent hole for the AC. Like I said it is way over to one side of the trailer. And I believe you tie in to the ducts from the top side On the roof just like the ones that are currently on the rig, but am a bit concerned about cutting a hole in the roof material and not finding the ducts where they are supposed to be, then I have to put on a new roof membrane.
If Fr said it's prewired for a 3rd AC then it would be where the vent is . if you choose a random location in the kitchen then you will also have to add support members for the AC along with finding the 120v around the vent and T-stat wire run them to the location you choose . you would most likely have to drop a ceiling panel to do the work to expose where everything is . When they set these units up for additional AC it's always at an existing vent.
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Old 09-01-2022, 08:26 AM   #19
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I have the same size Cardinal as OP's and I can tell you there have been times when my two A/C's don't completely keep up.
I am in NC and on the really hot and humid days they get pushed to the limits.

Why? pretty simple, lack of insulation in the build.
Come winter flip that to the opposite with heat.

My HOUSE a/c has trouble on really hot humid days.. in Florida

on the hottest part of the day ..... run your hand over the ceiling , slides walls ... find hot spots and work out how to get rid of them


(I'm too cheap to buy those in-fared cameras or mechanic thermometers)




If you're traveling and the trailer gets heat soaked... everything inside the trailer is HOT. It takes a LONG time for the heat to be removed from interior surfaces...
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Old 09-01-2022, 09:07 AM   #20
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A couple of questions first?

1. What year is your Cardinal?

2. What does the sales broacher for your model year state on a 3rd AC availability?

From what I have read and looked at you need some special electrical features to run a third AC in an RV. You may need to change to a soft start system for the AC's, + a power management system so, the AC 's are not all trying to start at the same time.

This summer which has been hot and humid in the mid-west, I was able to keep our Cedar Creek comfortable with just two AC.

I would run the AC fans on constant not automatic. The front AC fan was run at medium speed or high speed during the day with the temp set to 72F. The rear AC unit was set to 72F also, but the fan was run at low speed. The ceiling fan was usually set at low speed also in the summer mode. We also operated a floor fan that moved air as was needed. The temps in the unit were normally around 74F with a daytime temp in the +90'sF and humidity was in the 60% to low 70% range.

I also used a sunscreen attached to the awning to help shade the sun side in the afternoon time. As this was the predominant side for the sun shing on the trailer. All sunscreens were closed, and the night shads were also closed. This seems to keep the trailer relatively cool.

Another suggestion to help in keeping the trailer somewhat cool.
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