Try this first before you buy 2nd AC unit or bring your unit in for AC service.

[blw2]

yeah, half and Jamie....that's an interesting idea.
My first thought is that it'll have little to no effect.... the idea being that if there's no place for it to go down at the end, no matter how far down that is, that there'd be zero flow rate so no volume of air lost, and no significant btu loss.... basically the air in the dead end duct pressurizes to the point that no more air can get in....like a "virtual" plug.
BUT
the more I think about it, no doubt that ceiling to foam connection isn't air tight so there's very likely all sorts of leaks into mysterious ceiling cracks, crevices, and cavities.... resulting in some flow lost to the black hole, instead of on my sweating skin where I want it to be....

[Long & Winding road]

JamieGeek - So you could feel more air flow in the modified duct vs OEM? That sound good to me.

Darn it guys.... you keep making my "Mods list" grow longer every week I read stuff on this forum. LOL.

Just when I "thought" I was "almost" caught up. I guess I will never get caught up.... good thing I like tinkering.

[JamieGeek]

Originally Posted by Long & Winding road

JamieGeek - So you could feel more air flow in the modified duct vs OEM? That sound good to me.

Darn it guys.... you keep making my "Mods list" grow longer every week I read stuff on this forum. LOL.

Just when I "thought" I was "almost" caught up. I guess I will never get caught up.... good thing I like tinkering.

Yeah that is the thing: I tried just one (the front one right next to the door), turned on the A/C and checked the difference between it and the other front one. Just by feel you could tell more air was coming out my hacked duct.

The difference wasn't as dramatic in the rear--most likely due to the fact that the ones in the back are a long way from the A/C and there are two "middle" vents in between the rears and the A/C.

[Long & Winding road]

Good to know. I might check it out this weekend. Thanks.

[Long & Winding road]

Originally Posted by blw2

and side note...yeas, by front nose cone is similar to that earlier photo showing the thin outer wall with no insulation... and the back wall where it's radius up to the roof is the same way. Quite a few areas that could be better insulated...would help with the road noise too....

Blw2 - Did you remove the trip piece on the back wall "Radius" yourself? If so how does it remove? Just pop it off? I dont have my RV outside right now .... but is it just held on by staples (like everything else)? Was it easy to reinstall? I like to insulate that area but I dont want to mess anything up either.

[blw2]

Originally Posted by Long & Winding road

Blw2 - Did you remove the trip piece on the back wall "Radius" yourself? If so how does it remove? Just pop it off? I dont have my RV outside right now .... but is it just held on by staples (like everything else)? Was it easy to reinstall? I like to insulate that area but I dont want to mess anything up either.

Well..... the first time it fell down on its own, thanks to Louisiana's wonderful road maintenance program....
It was basically held up with some two sided tape like stuff and a few staples. On the road so I jury rigged it back up in a similar fashion. A few weeks ago I pulled it down to replace my review camera. I had it stuck up there better than the factory it seems...anyway, The wiring and connector for the camera is under there, as well as the rear clearance light wiring.
Anyway, mine is just a simple flat piece of some sort of hardboard or something, maybe 6-8 inches wide. Small decorative molding trim out the long top and bottom edges.
It would be better I think if the molding were more firmly attached, and the trim panel snapped in tight between.

anyway, the point is, mine is not up there in any sort of elegant fashion, so it just takes a little fenagling. Sadly, I didn't take a photo...

[halfprice]

Originally Posted by JamieGeek

Yeah that is the thing: I tried just one (the front one right next to the door), turned on the A/C and checked the difference between it and the other front one. Just by feel you could tell more air was coming out my hacked duct.

The difference wasn't as dramatic in the rear--most likely due to the fact that the ones in the back are a long way from the A/C and there are two "middle" vents in between the rears and the A/C.

I got the same results as Jamie. Total cost was $7 for the expanding foam insulation.

Jerry

[JamieGeek]

Originally Posted by halfprice

I got the same results as Jamie. Total cost was $7 for the expanding foam insulation.

Jerry

If this works well I may pick up some foam blocks at a craft store and sculpt a ramp for a more permanent solution than the duct tape. (I figure I would measure the space, sculpt a block in a wedge to fit, then cut it into 3 pieces to get it up there).

[Long & Winding road]

Thanks Blw2, I will look at mine. Perhaps I will use some double sided tape and some small nails or srews in the corners for support.

[Diemaster]

so i apologize if its been said before. but im not going to spend a while day re-reading an 10+ page thread but i was starting to do the mods and found the temp sensor was already at the high point of the coils. ill start to seal up the vents but im not sure if this is good or not. ill get a AC thermometer to get intake and outtake temps.

[BradnKaren]

We had the vent ends filled with foam at the dealer, who suggested it. Thor covered it under warranty. It helped. I think it also provides some insulation in the roof and helps to keep the heat out.

[gmtech16450yz]

Hey guys a couple heads-up or ideas for you on the vents...

Make sure you use the higher density or "tight" expanding foam, your results will be much better.

Use an insulation knife or similar so shape/cut the foam.

Remove the black plastic rings from the vents and cut the edges of the foam WAY down around the vent openings. That alone will help greatly with reducing restrictions. (Pics below.)

Here's a little something else I found out that made my decision on what second AC unit to buy. The rear roof vent, at least in my 27.7 Vegas, can be made to feed the vent system. In other words, if you put a second AC unit in, you can have it feed into the entire vent system easily. This, to me at least, is huge. That means I can put a heat pump Mach 8 in the back roof vent and duct it into the stock ducts. Not only will I be able to run both AC's through the ducts and out the ceiling panels, I'll be able to cool OR HEAT the entire coach from EITHER unit. That will be cool! (sorry.)

When both AC units are running, I'll basically have 640cfm airflow through the vent system, which I severely modified for better airflow. It should be like a frozen tornado! Yes! Exactly what I want.

The mods to the front 15k unit are done, it's gonna be whatever it's gonna be. I ended up adding 420cfm worth of electric fans to the condenser case and built a duct for the main fan so it's now a "ducted" fan. Those two mods HUGELY increased the airflow through the condenser core. I also sealed up all the air leaks in the evap side and optimized the squirrel cage fan and area. I finally insulated the whole evap box with multiple layers of foam/fiberglass and dynamat. In theory it should be much more efficient and tolerant of super high roof temps, but time will tell for sure how much difference it all makes. Obviously it was a lot of work and not something most anyone else would want to do. I simply wanted to get the most I could out of the 15k, and that's what I got by doing the mods I did. The final thing I did was to add an outlet vent to the ceiling panel. I might actually add an inlet one on the other side too. By using one of the black plastic vent rings I can make it feed air into the evap inlet and still retain the outlet vent at the front of the panel.

I'm most likely going to order a 13.5k Mach 8 plus heat pump to put in the back vent. Even if the front 15k works way better, I still want a ton of cooling power because it will mean the generator will have to run half as long to cool the unit back down after it sits in the sun all day. We rarely have hookups so for our use optimizing AC efficiency while on generator is the number 1 priority. That's also not the case for a lot of you.

[Long & Winding road]

Awesome info. Let us know your results (esp output temp improvements). Any easy tips for us that just want to improve air flow on the roof or though the condenser inside?

Will your plastic shroud fit over your pregnant air box on the roof? LOL. I thought about adding another layer on mine but I was not sure if it would fit or if it was really needed.

[Long & Winding road]

GM Tech - I did your Vent mod today! WOW - the two front and two rear vents really blow the air now. I hate to be over optimistic but I would guess 40% more (like to put 50% more but im trying to be conservative). I used some frost king to block the air flow as each end of duct work.

[gmtech16450yz]

Originally Posted by Long & Winding road

GM Tech - I did your Vent mod today! WOW - the two front and two rear vents really blow the air now. I hate to be over optimistic but I would guess 40% more (like to put 50% more but im trying to be conservative). I used some frost king to block the air flow as each end of duct work.

Nice! Yeah I think there's a ton of room for improvement in the way Thor did those ducts. I ran my finished AC tonight for awhile and I'm VERY happy with the improvements.

Airflow into and out of the unit is drastically increased, tested and verified by watching amperage and by putting an airflow meter across the inlet and outlet. I did add the second vent to the ceiling panel, differently than you'd expect though. I modified the ceiling panel duct routing so that the outlet air comes out of the two added vents and the inlet air not only comes in the stock locations, but also comes in from the front opening. It made a huge difference in how much air is going in and out of the unit. I even moved the control box to the side of the evaporator core area so it's out of the airflow.

I monitored my inlet and outlet temps while turning my added electric fans on and off. Outlet temps dropped 3-4 degrees almost immediately when the electric fans are turned on. Outlet temps went back up after turning fans off. They work, same as they did 25 years ago on that old Coleman roof air. Everything I did was incremental, meaning there wasn't one mod that made it completely different, just a bunch of little optimizations that combine to make the entire unit work better.

I need another hot weekend to compare before and after temps, hopefully this next weekend we'll take the boat out again. I did get some temp numbers for you guys already though, 72 degree inlet air and 38 degree outlet air with WAY more airflow (which normally raises the outlet temps)! I have no idea how it will do in super hot conditions, but I'll take that 34 degree split for now. It absolutely will work better in super hot conditions. How much? We'll see.

I did order a 13.5k Mach 8 Plus -heat pump and condensate pump version for the back vent location. I'm going to duct it into the stock ducts, when the front 15k or the back 13.5k are on by themselves, they'll be able to feed the entire duct system from either end. When they're both on at the same time, it's gonna be a cr@pload of really cold airflow coming out of all the duct vents, the extra vents I added on the front 15k and the extra vents I'll put on the rear 13.5k too! I can't wait to get in another 100+ degree situation and let the inside temps get to 99 degrees like they were. My guess is I'll be able to have the inside coach temps down into the '70's in probably an hour or so after starting at 99 degrees inside. We ran that 15k for 10 hours straight after it was 99 degrees inside the coach and the best it did was 80-82 degrees. F that.

The other thing that will be nice is I can run the rear Mach 8 in heat pump mode and have that warm air come out all of the coach vents. That will be a nice addition to the gas furnace when it's cold out. When on hookups, I'll be able to run the heat pump on the quiet low fan speed and leave it on all night instead of having to use the propane furnace. It won't put out the amount of heat the furnace will, but it will distribute it through the coach a little better.

[Long & Winding road]

GM Tech - I like what you did with your cover inside. How did you mod the inside part for the return side? I guess you will have to make sure that one is open all the time to maximize air flow inbound.

Do you think insulating around the condenser fan shroud (like your picture shows) makes a difference?

Im looking for some more easy mods that I can do myself. Like you said they all add up after a while. So 2% here 3% there sound good to me as long as its an improvement.

I might hook up another fan or two on the shroud - so let us know more details when you can on that mod alone.

Any other easy mods/insulating that you would suggest that we have not talked about already?

Your inside ceil register vent mod was awesome..... cant wait to try it out when it warms up some.

Thanks.

[gmtech16450yz]

Originally Posted by Long & Winding road

GM Tech - I like what you did with your cover inside. How did you mod the inside part for the return side? I guess you will have to make sure that one is open all the time to maximize air flow inbound.

I basically stopped the outlet duct by cutting off the end and blocking it. That keeps the outlet air in the area where the two round added vents are. The area in front where the original outlet that slides open and closed, I covered that opening with black speaker material and glued the slide so it stays open all the time. When the AC is running, I put a piece of paper up to that front opening and it sucked the paper tight to the opening. That means it's definitely sucking in extra air there. I can also see restrictions in the inlet or outlet sides simply by watching the amperage draw change. Just closing a vent or two will change the amperage draw of the AC fan motor. What you're shooting for is actually higher amperage, low amperage means the fan is "cavitating" and not pulling air. Blocking the extra inlet vent I made makes the amperage draw change from 3.2 to 3.0 amps. Coleman's ceiling assembly MOST DEFINITELY is not optimized for good inlet or outlet airflow. Amperage draw changes drastically when you run the AC without the ceiling panel in place. Amperage even raises when you take the inlet filters out, meaning better airflow. 320 cfm is a LOT of airflow and needs big openings to keep it moving freely.

Do you think insulating around the condenser fan shroud (like your picture shows) makes a difference?

Lol. It makes no difference at all. The dynamat around the fan shroud is for strength and stability of the shroud, nothing more. It's fairly thin sheet metal riveted together. I made that shroud myself, Coleman isn't smart enough to realize a fan with huge pitched blades like that will not be very efficient when it's inlet and outlet sides are only separated by a 1/4 inch bend of sheet metal. Making it ducted like I did by adding that shroud greatly increases the efficiency of the fan.

Im looking for some more easy mods that I can do myself. Like you said they all add up after a while. So 2% here 3% there sound good to me as long as its an improvement.

I might hook up another fan or two on the shroud - so let us know more details when you can on that mod alone.

This is unfortunately another "don't try this at home" mod. haha. It obviously can be done, but it's not super easy. I originally wanted to use 110volt AC fans, but couldn't find any with a high enough static pressure so I ended up using 12 volt fans. You have to think about the physics of fluid dynamics when you're doing silly stuff like this or you can make things WAY worse really quickly. If the fans you add into a shroud like this aren't strong enough to pull against the negative pressure of the main fan, you'll end up actually pulling air in through them backwards. And also, if they aren't running, they'll pull air in through them backwards instead of pulling that air through the condenser. Obviously it can be done and if done right does absolutely make a difference, but spec'ing the fans and engineering the 12 volt power to them might be more than some of you guys want to take on. I put a relay near the thermostat that pulls higher amperage 12 volt power to feed the fans when the thermostat triggers the compressor to run. It's all automatic so I don't have to worry about turning extra fans on or off. There's a TON of airflow coming out of that shrouding around the roof AC unit now! And quite a bit blowing directly on the compressor also, which needs it since it's trying to compress 400+ psi refrigerant.


Any other easy mods/insulating that you would suggest that we have not talked about already?

Of all the super easy mods, the ceiling panel I think might be the biggest bang for the buck item to concentrate on. Like many on here have already figured out, simply adding a down vent directly below the outlet fan makes a huge difference. If I wanted a project to make some extra cash, I might consider selling modded ceiling panels. lol. Doing the intake side mods are a little harder for the do-it-yourselfer, but also makes a really big difference in the AC performance.

Your inside ceil register vent mod was awesome..... cant wait to try it out when it warms up some.

Thanks.

Thanks to all that have kept contributing and reading this thread, we've ALL learned some good stuff! I can't wait to get my new Mach 8 Plus so I can see how the totally different design compares to the decades old models like my 15k. And I can't wait to get into some horrible hot weather so I can turn both units on full blast and have a blizzard/tornado in my Vegas! lol. I just told my wife after seeing how the mods worked out on the 15k, "We will NEVER AGAIN have a problem trying to stay cool in this coach". She liked that.

More pics for above info...

[Long & Winding road]

Thanks for the info. I might try to mod the Colman interior vent cover like yours down the road. I think I will wait for some hot weather to kick in again to see how my mods are doing. My AC is working much better this year over last year so anything else is a bonus. The key is heat managment with any RV. Keep all the heat out is the keep.

I Might add one or two more vents to the ceiling near the cockpit area (esp after I feel the increased are flow with your vent mod). Any thoughts on that? Will it weaken the air flow on the other registers were I wont see any gain? Or perhaps it will help since the cockpit area is the hotest part of the RV?

[gmtech16450yz]

Originally Posted by Long & Winding road

Thanks for the info. I might try to mod the Colman interior vent cover like yours down the road. I think I will wait for some hot weather to kick in again to see how my mods are doing. My AC is working much better this year over last year so anything else is a bonus. The key is heat managment with any RV. Keep all the heat out is the keep.

I Might add one or two more vents to the ceiling near the cockpit area (esp after I feel the increased are flow with your vent mod). Any thoughts on that? Will it weaken the air flow on the other registers were I wont see any gain? Or perhaps it will help since the cockpit area is the hotest part of the RV?

The cool (ugh. not again.) thing about the vent system is that they're all able to be closed. I really like that. So if you add a bunch of extra vents at the front or in the ceiling panel itself, you can always close them if you need to.

Yeah, if I have ALL the vents open, the airflow say at the very back where the bedroom vents are will be weaker. But if you're in the very back, maybe in bed getting sweaty (lol. tmi.), you can close off every single vent except for the two over the back bed and have tons of airflow where you need it. In my opinion, adding extra vents to the system or the ceiling panel is a mod with really no downsides. These roof AC's don't run super cold evap temps, and increasing evap airflow doesn't effect the evap temps that drastically. That means you need a ton of air exchange in the entire coach to cool it down since the temp drop is so little (15-20 degrees lower than intake temps). If the output temps were 40 degrees below intake temps, it wouldn't take that much airflow to cool things down. That's not how these systems work.

[carlgorski]

Originally Posted by gmtech16450yz

The cool (ugh. not again.) thing about the vent system is that they're all able to be closed. I really like that. So if you add a bunch of extra vents at the front or in the ceiling panel itself, you can always close them if you need to.



Yeah, if I have ALL the vents open, the airflow say at the very back where the bedroom vents are will be weaker. But if you're in the very back, maybe in bed getting sweaty (lol. tmi.), you can close off every single vent except for the two over the back bed and have tons of airflow where you need it. In my opinion, adding extra vents to the system or the ceiling panel is a mod with really no downsides. These roof AC's don't run super cold evap temps, and increasing evap airflow doesn't effect the evap temps that drastically. That means you need a ton of air exchange in the entire coach to cool it down since the temp drop is so little (15-20 degrees lower than intake temps). If the output temps were 40 degrees below intake temps, it wouldn't take that much airflow to cool things down. That's not how these systems work.

Where did you tap in to power fans?