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Old 08-01-2021, 08:46 AM   #1
jdarwin
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AC register positions

We have a 3931FB. It has 2 registers in the master bath, 2 in the bedroom, 1 in the half bath and 4 in the living area. I’m looking for advice on how to position the registers to keep the rig cool with 100+ days here in Texas. By the afternoon it’s 100 outside and 90 in the bedroom and master bath. It’s around 85 downstairs. We supplement with a high volume fan to blow air from down stairs up into those rooms. The rig does sit in the open and gets direct sun all day. We put out the awnings in the morning to keep the sun off as much as possible. Should I be looking for a shaded site? Appreciate your input.
 
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Old 08-01-2021, 08:53 AM   #2
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You don't say if you have one or two AC's. Regardless, the first thing to do is to cut every other fin off the supply vents that you want more air to come out of. You need to make sure that the return air vents to your furnace are covered (most of us cut poster board or something similar and put it behind them). Next cover any windows you don't use with the silver bubble insulation. We also insulate the outside walls of our cabinets. And certainly, if you can move to a shaded spot do so.
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Old 08-01-2021, 09:14 AM   #3
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I talked to the Product Manager for Keystone. Change coming in White AC units on the roof. 20% more efficient?? Who knows. With three units we’ve managed to stay cool making the western run June-August this year. Just can’t complain about noise inside. Had to fight freeze up on rear and shut downs on front two. Home in two weeks and time will be spent up on roof trying stuff.
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Old 08-01-2021, 09:52 AM   #4
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DQDick, we have 2 Dometic 15K BTU units. They are covered with a black plastic shroud. One is mounted on the roof, in the front of the rig and the other at the rear. Where are the return air vents for the furnace? I see the vents in the floor but can’t find the return air air to the furnace.
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Old 08-01-2021, 10:41 AM   #5
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John, I don't have your floor plan schematics but the normal place for the return air vents for the furnace are in the risers of the steps going up to the front living room or to the front bedroom. During the summer and hot weather cover them with some bubble wrap insulation or even cardboard on the back of the risers. The reason for the back is so it is not so obvious that the vents are covered. The risers normally can be taken off by removing several screws on the front side. Also Dick mentioned taking every other fin out of the ceiling vents. You an also remove the vents, use metal tape to seal the space between the ceiling and the ducting. This stops the cool/cold air from going into the attic (space between the roof and the ceiling). Also when you have the vents down or out, check to see if the tube that goes up into the ducting is to high in the ducting. Normally, this is the case and the only space that allows air from the duct into the vent is about a 1/2-3/4" at the top of the duct. If you cut off about an inch of the tubing going into the duct from the vent you will increase the amount of air that is allowed to flow from the duct to each ceiling vent. Also, if you have not checked to see if your return ducts for your A/C's has collapsed, I suggest you do that also. Take the return vent cover off and take a mirror and a flashlight and see if the vent has collapsed. If it has, there are numerous posts here on the Forum telling you how to take care of that problem. If you can't find it, let me know via PM and I'll explain the process of curing that problem. Remember the RV A/C's are not like a stick and brick's A/C and will only cool a unit down about 20 degrees cooler than ambient temp. I have done several other things to insulate the unit and keep it cooler. I can give you those ideas also if you like. Good luck and hope you can cool things down some.
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Old 08-01-2021, 11:31 AM   #6
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In addition to all the above...
Take the cover off the unit on the roof and make sure the cooling and the heat exchanger fins are clean.
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Old 08-01-2021, 01:06 PM   #7
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Rondo, I found the return furnace vents at the stairs. I removed the air conditioner vents. Are you talking about adding extra foil where there is already some? I also took a picture inside the actual air conditioning vent and you can see what it looks like. Regarding the AC vents, If I understand you correctly, I would be cutting off part of the vent stack that goes into the ceiling.
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Old 08-01-2021, 01:55 PM   #8
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Your are correct. I've always reduced the stack and removed everyother fin on the vent it'self on all our rigs. Both of our current rigs have black covers and we are fully able to maintain temps in Kansas heat and humidity. The last two weeks have had heat indexes above 105 each day.
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Old 08-01-2021, 03:16 PM   #9
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It is great having wheels on our rigs. They allow us to move somewhere with better weather if its too hot or cold.
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Old 08-18-2021, 09:28 PM   #10
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I just purchased a 2021 Montana high country. After looking into it I’m beginning to think it is a Montana trait as a pertains to the air-conditioning. What you described as it pertains to cooling the front and the main cabin is exactly what is happening with this brand new camper. I have owned six other brands of fifth wheels all of them 40+ feet long and I’ve never had an issue with cooling down the unit. Ever. And I use and live in the same conditions. Not until I bought this new Montana has it been an issue. The dealership I bought it from basically told me this is an ongoing issue with Montana and has been. Their suggestion and solution is for me to put a third air conditioner in the unit. Now, this is not the only issue with this camper so I do not know how long I will keep it. But, if I do keep it then I will be putting in third one in the unit so I stop fighting with it.
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Old 08-18-2022, 05:04 AM   #11
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Quote:
Originally Posted by jdarwin View Post
Attachment 9835

Attachment 9836

Attachment 9837

Rondo, I found the return furnace vents at the stairs. I removed the air conditioner vents. Are you talking about adding extra foil where there is already some? I also took a picture inside the actual air conditioning vent and you can see what it looks like. Regarding the AC vents, If I understand you correctly, I would be cutting off part of the vent stack that goes into the ceiling.
So... is that normal for hot air to be coming out of the stairs with the A/C on?
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Old 08-18-2022, 05:52 AM   #12
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Originally Posted by HondoSwatdog View Post
So... is that normal for hot air to be coming out of the stairs with the A/C on?
If you have air coming in through the stairs with the AC on, you have a return air flow restriction in the air return vents in the ceiling.
Open them, clean the filters, inspect them to be sure they are properly sealed from the attic.
Most likely you have collapsed return ducts.

IF you have collapsed ducts, many have successfully installed PVC pipe in the return to open it up.
In this video I would have installed longer pieces of pipe.
Montana HC return duct mod
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Old 08-18-2022, 06:24 AM   #13
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As long as I've been reading RV related forums, it seems there has always been a temperature difference in fifth wheels between the upper floor and the bottom floor. That is one reason why the front living room model was attractive for us. By having no walls between the upper level and the bottom level, there would not be any difference in temperature between the two. Not!

Even with the open concept between the upper front living room and the lower middle kitchen area, there is always a temperature difference. Regardless of heat or air conditioning, the upper seems to be always warmer. We keep fans blowing, the ceiling fan, which circulates air for both kitchen and upper living room, and even with that, there is still a difference in that 2.5 feet rise and moving from 10 foot ceilings to 6 foot ceilings.

Especially in the winter, there was always a cold draft on the bottom level floor, and in the Summer, it's a hot draft.

One day, I pulled the back wall out of the pass-through cargo area under the front and I was shocked at all the light I could see. And then I also looked at the furnace and realized there really was no duck work on the air return. The air return pulls the air from under the steps leading to the upper level (kitchen - living room), as well as all that open space under the floor and in that gigantic cavity behind that wall.

That means, when either the furnace (or) the air conditioner is running, both are pulling return air from under that open cavity. The air conditioner return is sucking hot air through all those open cracks and gaps where your underbelly Chloroplast is not sealed. Not to mention all the gaps and cracks in the construction.

When I saw all that light, all those pin-holes, all those cracks, I then understood why we always had a bad draft on the lower level kitchen floor. It was coming from under the steps to the upper level.

That resulted in purchasing about 20 tubes of Liquid Nails, purchasing a nice foam exercise floor mat, and a new caulking gun. After a couple days of filling all those holes, gaps, and pin holes, I put the basement wall back on. And.... No draft any more!

Not only did this cut my propane usage for heat tremendously, it also made a huge difference in the the Summer on the cooling effect of the air conditioner.

Folks above have the right idea about covering that return under your steps to the upper level. But, if you want to fix it permanently, then take the time to seal up all those cracks, holes, pin-holes, and gaps in that open cavity area. That will eliminate a lot of your problems.

And oh, by the way.... even doing this, there is still a temperature difference between the upper level and the bottom level. It's just the nature of the beast. But, it's not as great as it use to be.

The real positives are: No draft any more on the bottom level floor. Air Conditioning seems cooler. Furnace runs less and the entire camper feels warmer in cold weather.
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