I was shocked at how my A/C air handling is done, and what I did to fix it.

The A/C in my Rockwood Signature Ultralight has always had problems cooling the unit to the point where I thought that the A/C was broken or defective in some way. The air coming out of the ceiling registers was never more than barely cool, and the air flow very weak.  I thought I needed a second A/C unit so made a modification to the electrical system to allow the addition of a heat pump.

The A/C unit has also dripped water out of from the inside cover and I thought it was some kind of condensation (wrong).  I saw a post where someone added a marine observation port to allow dumping of the cold air directly into the rig, and also saw mention of sealing the duct work to prevent leaks, so I decided to remove the cover and see what I could do to implement some of these fixes. I was also perplexed as to why the A/C was dripping while it was turned off on a foggy night.

I was shocked to see that one bolt was backed out nearly 2 inches, and all were loose - this is why water was dripping. It was probably my bad not checking the bolts, but this dripping was occurring from day one so it could have been poor assembly.

Next, I looked for ducts, but found none. I ran my hand into two slit-like spaces leading into the roof space and concluded that this must be the "ducting" to the air outlets, and was correct. Evidently there are no ducts in my ceiling - the A/C air simply dumps right into the space between the roof and the ceiling (this explains why I felt air coming out of the light fixtures when the A/C is running). Sure there is 3/8 inch styrofoam on the interior of the ceiling and another layer on the inside of the roof, but really? ... using the entire roof as the air ducting system? No wonder the air flow was weak, and temperature was barely cool.

I read another post where someone measured the temperature of their roof to be 191 degrees on a sunny day.  I cannot believe that a 3/8 inch layer of styrofoam will do much of anything to keep the ceiling space from becoming really hot and storing that energy in everything in the ceiling, like the light fixtures, structural supports, etc. In effect, the A/C had to cool all structural elements down before it much of anything to cool the rig.

It looks like this A/C unit was designed for a TT because there is a large grid where air is supposed to come out. Rockwood had covered this with a sheet metal plate which deflected the cold air into the slits leading to the ceiling space (see pics). They could then punch a hole anywhere in the ceiling to tap into the "duct" because essentially the entire ceiling is one big duct (talk about a waste of energy).

Because the ceiling air outlets are essentially only eye candy with little to no function, I took off the sheet metal in the A/C cover and was amazed at the difference. A huge volume of icy cold air now comes out of the unit, and in a test yesterday I was able to get the rig down to 65 degrees before the A/C automatically shut off.  I've never been able to get the rig that cold under these weather conditions. Sure, I have lost air distribution through the ceiling, but I have gained more than enough cold air to make the rig comfortable.

The take home lesson - if you are having problems with your rig cooling, take off the A/C cover and see what surprises the manufacturer has in store for you. I've learned that my rig looks beautiful on the inside, but those looks come at the expense of function.

The yellow arrow points to one of the slit-like opening into the ceiling space]

This is how I discovered that there are no ducts - I fed a tape measure into the slit and worked it back toward an air outlet - no obstructions of any kind and I could move the tape in all directions.)

This shows the interior A/C cover where the air was supposed to come out in the original A/C design, and you can see black foam through the grid


This is the interior of the cover - you can see the sheet metal plate which I took off. The A/C unit now blows huge quantities of icy cold air - a gigantic contrast to the barely cool air that has always come out of the unit. I was more than willing to give up poor air distribution for cold air.

So if I understand you right you took off a plate and let more air flow into the roof space from your AC to solve the problem?  You didn't try to add ducts?  Wouldn't that still be inefficient?  I am truly amazed that an RV could be designed this way.  Thanks for sharing this info.

Yes, you are correct in that I took off a plate, but I closed off the slits to the roof space so all the air comes into the rig through the cover grid (nothing now goes into the ducting system). I don't think I can add ducts because the space is only 1 inch tall, and I would have no way to fish ducting to the air registers in the ceiling.  I agree that it is inefficient in the sense that I do not direct air flow into all areas of the rig, but the way it was, I was already hot in all parts of the fiver, uncomfortably so, and I (and more importantly the wife  ;D ) am much happier having our main living area cold during the hot days. In a way, cooling is more efficient now because I am not cooling down the ceiling (or ducts) in any way.

Why does the ducting have to be inside the ceiling? Couldn't you surface mount them?

Thanks for posting those pictures.
That looks like the same Coleman Mach unit that I have.
I have never taken that shroud completely off, but plan to now ASAP.

A can say that in my case, the styrofoam is routed to form channels between the ceiling skin and the Styrofoam insulating layer above.  You can see the channels through the AC diffusers.  I have the same circular ones that you do.  It looks like two parallel channels running front to back on the coach.  I've always assumed that these channels were sealed from each other and sealed from the rest of the ceiling areas....maybe they're not. 

Sounds like yours doesn't have the duct channels at all, and it's just an even void across the entire ceiling.  Is that right?  Surely the ceiling is attached to something?

Using the space between the ceiling and roof as a plenum for air distribution is fairly common in large commercial buildings.  As you stated, the heat gain thru the roof kills the efficiency. 

Good point SeilerBird - hadn't thought of that, but will keep it in mind should the wife complain about it being too hot in the bedroom  ;D

I don't know if there are channels or if there are, if they are sealed from each other. I kind of doubt that there is much sealing because I feel air coming out of the ceiling light fixtures when the A/C is running. However, there mist be some kind of structural support between the ceiling and roof - unfortunately the air slits are too restrictive for me to get my tape measure at those angles.  I'm planning to remove the A/C next year to inspect and reseal the opening and will see what I can discover at that time.

Yesterday when I demonstrated the large increase in cold air flow, the wife squealed in delight (it was a surprise - she had no idea I was doing this) - as the saying goes, happy wife, happy life.  ;D

As an afterthought, we use a couple of small fans to keep the air moving around our trailer. Since your ducts in the bedroom are apparently just decoration, a fan to blow the cooler air from the living area to the bedroom may be of some help.

Where your piece of sheet metal is, mine is open.  I have a sliding cover that can open and close to allow that air to blast down.  It is really a treat when first setting up and getting the rig cooled down.  I would like to get more airflow through the "ducts" though.

Pz, have you thought about calling Rockwood (part of Forest River) and inquiring about what appears to be really shoddy workmanship?  It sounds like an incredibly poor design to me.  You also might find a group of Rockwood owners with whom you can discuss the issue and compare the various units.  There appears to be a Forest River Owners group so that might be a start.

ArdraF

A point that has been missed is that the air layer between the ceiling and roof contributes significantly to insulating the trailer.  That contribution is lost completely when that air is circulated.

Ernie

Note: Insulation materials work primarily because the trapped air within the material is a relatively poor conducter of heat. In a perfect world we'd have a vacuum in those spaces since it doesn't conduct heat at all (radiated heat is partly controlled by using reflecting surfaces in a vacuum bottle.)

Patnsuzanne said:

As an afterthought, we use a couple of small fans to keep the air moving around our trailer. Since your ducts in the bedroom are apparently just decoration, a fan to blow the cooler air from the living area to the bedroom may be of some help.

Click to expand...

Thanks Patnsuzanne - I am planning something similar - have installed 2 Fantastic vents that will draw cold air to the extreme parts of the rig.

edjunior said:

Where your piece of sheet metal is, mine is open.  I have a sliding cover that can open and close to allow that air to blast down.  It is really a treat when first setting up and getting the rig cooled down.  I would like to get more airflow through the "ducts" though.

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At first I thought I'd like to have control of air flow at the shroud, but in retrospect, I'd rather have maximum cooling power since the rig is not well insulated and it is hard to keep it comfortable in 100 degree weather. My two "ducts" are about 10 inches wide and 1 inch tall, and while it would be nice to be able to have good air flow through them, the fact that the ceiling is so hot in the sun makes the air come out luke-warm anyway. The other problem is that there must be significant air leaks - I feel air coming out of the ceiling lights when the A/C is running, and those lights are not on the path of the A/C air channels.

ArdraF said:

Pz, have you thought about calling Rockwood (part of Forest River) and inquiring about what appears to be really shoddy workmanship?  It sounds like an incredibly poor design to me.  You also might find a group of Rockwood owners with whom you can discuss the issue and compare the various units.  There appears to be a Forest River Owners group so that might be a start.

ArdraF

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Thanks Audra - I did connect with a Forest River group and one member sent me a PDF image of how the company builds it's ceilings. Evidently they have two channels running the length of the rig which is designed to conduct air to the ceiling registers. Unfortunately they are lined with 1/2 inch thick Styrofoam, so it takes a long time in the sun to cool the ceiling enough so that cool air comes out of the registers. In fact, in full sun I cannot ever get cold air out of the registers - the sun is heating the ceiling faster than the A/C can cool it.

Ernie n Tara said:

A point that has been missed is that the air layer between the ceiling and roof contributes significantly to insulating the trailer.  That contribution is lost completely when that air is circulated.

Ernie

Note: Insulation materials work primarily because the trapped air within the material is a relatively poor conducter of heat. In a perfect world we'd have a vacuum in those spaces since it doesn't conduct heat at all (radiated heat is partly controlled by using reflecting surfaces in a vacuum bottle.)

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You're absolutely correct Ernie - I wish that I could seal the ceiling air spaces like a vacuum bottle. I'll bet that would reduce my heat transfer most significantly.

just thinking out loud here....
as  an alternative thought, I'm wondering how it would be if you were to open up the holes into those two duct channels so that more air can move as opposed to it squeezing through that little crack.....and while at it close off the rest of the little crack that's not into the air duct channels to limit how much is going into the non-ducted space.

When i get a chance to open mine up, I figure I'll look at it with that idea in mind first.

Having seen it first hand, what our your thoughts based on what you saw?

That is one of the worst designs I have ever seen pz. You are spot on with your diagnosis and fixes. IMHO you need to get the most cold air as possible, into the living area of the rig.  While a second AC may be an option, you can make the decision after you try out the rig with the newly directed cold air ducts. Let us know what you decide.

blw2 said:

just thinking out loud here....
as  an alternative thought, I'm wondering how it would be if you were to open up the holes into those two duct channels so that more air can move as opposed to it squeezing through that little crack.....and while at it close off the rest of the little crack that's not into the air duct channels to limit how much is going into the non-ducted space.

When i get a chance to open mine up, I figure I'll look at it with that idea in mind first.

Having seen it first hand, what our your thoughts based on what you saw?

Click to expand...

Brad - when I first looked at the slits leading into what I finally realized are the duct channels I was thinking the same - try to open them up, but the space is only about an inch high - I can barely get my hand into the space. If I were to try to open it up, I would be taking away what little insulation I have on the inside of the room and ceiling, which is a pathetic 1/2 inch of Styrofoam. That thin slit is the ducting in my rig. As to the leaks into the non-ducted space, I'm suspicious there are leaks (who know how many) away from the opening near the A/C because I'm getting significant air flow through a light housing in the back of the living area.  Now I'm suspicious that there are many leaks, and my suspicion arises mainly because I'm doing other repairs and mods. For instance, my CO/propane detector needed to be replaced - I put in a new one, but because the factory had cut the hole too big, they put in a piece of plywood as a backer for the screw. The plywood was not attached and fell to the floor inside the wall space - fortunately the detector is near the floor. Unfortunately I had to unscrew a different wall panel inside a cabinet just to get my hand in to hold the loose piece of plywood so I could screw in the detector.  I also removed my old analog thermostat to replace it with a Honeywell - imagine my astonishment to discover they did the same thing on the opening for the thermostat wires!  Hole too big, and someone had put in a piece of the wall paneling as a backer.  These are not the only examples, only the latest ones, so I'm skeptical that I can do anything with the built-in ducts to make anything any better. I hope when you open yours you'll discover better build quality that what I'm discovering.

SargeW said:

That is one of the worst designs I have ever seen pz. You are spot on with your diagnosis and fixes. IMHO you need to get the most cold air as possible, into the living area of the rig.  While a second AC may be an option, you can make the decision after you try out the rig with the newly directed cold air ducts. Let us know what you decide.

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Marty - I ( and more importantly my wife  ;D ) totally agree with you - we need to get in as much cold air as possible. Fortunately the A/C is in the middle of the rig and all the cold air spreads out fore and aft quite easily. I ended up plugging the slits to the ducts and removing the sheet metal cover to the air flow grid - now 100% of the cold air goes straight down to the floor.  Fortunately due to the position of the A/C unit it does not blow right on to us because the wind is quite stiff! Before doing this modification, our A/C was so poor we actually missed our old entry level 23-foot TT because the A/C blew down such a large volume of cold air - now we have the same.  I'm confident that we will at least have better cooling power.

However, a few weeks ago I did another mod - we have a 30A rig so I made some changes so I could put in a portable 12,500 BTU heat pump, so now we should have plenty of cooling power with both units running.

I have thought for some time that our a/c is the same.  The air comes out through the ceiling light fixtures also.  We haven't noticed a big loss of cold air though, but it sure is loud.

Just to spruce up the temperature control a bit more, I replaced the original analog thermostat with a residential Honeywell digital unit.  It was basically plug and play once you get the wiring right - the whole project tool all of about 30 minutes.

The original Coleman Mach compared to the New digital on the right. The digital uses two AA batteries as the power source.

After removing the Coleman, these are the original six wires. The new digital does not have a hi/lo fan speed setting, so I did not use all the wires - only four, and capped off the gray and blue.

Here the wires are in place, and the rest tucked back into the wall. Red is the original 12V, yellow is the A/C, white is the furnace, and green is the high fan speed.

The finished install - works perfectly, keeps the temperature way better, and best of all, I need not futz around with those tiny micro control switches any more!

pz said:

Just to spruce up the temperature control a bit more, I replaced the original analog thermostat with a residential Honeywell digital unit.  It was basically plug and play once you get the wiring right - the whole project tool all of about 30 minutes.

The original Coleman Mach compared to the New digital on the right. The digital uses two AA batteries as the power source.

After removing the Coleman, these are the original six wires. The new digital does not have a hi/lo fan speed setting, so I did not use all the wires - only four, and capped off the gray and blue.

Here the wires are in place, and the rest tucked back into the wall. Red is the original 12V, yellow is the A/C, white is the furnace, and green is the high fan speed.

The finished install - works perfectly, keeps the temperature way better, and best of all, I need not futz around with those tiny micro control switches any more!

Click to expand...

Just to be clear since you did not say which two wires did you not use?
It is clear the Yellow and green were used but then you show a red which is jumped to a striped wire Is that the red in your final wiring and the white shows a blue wire jumped. which white did you use?

I think all the thick wires are part of the original coach wiring, and all the thin wires were formerly part of the old Coleman thermostat. I did not make any of those connections - I just pulled them out of the wall the way you see in the diagram, and left the parts of the thin Coleman wires in place to be sure I did not mess up the colors.

Yes, the red wire in the second photo is connected to a white and orange wire - The red wire was part of the original thermostat which the factory had connected to the thick white/orange striped wire. This red wire is the one connected to the new thermostat connector block

The blue wire is connected to a thick white wire. I capped off this wire and stuffed it back into the opening. This wire is not used.

The gray wire is the low fan speed wire, and I did not use that either because the new thermostat does not offer high/low fan speed switches.  One could use this wire if they wanted to install some kind of toggle (I saw a good YouTube video on this), but because I always have my fans running on high, I did not use this wire.

So if you look closely in the second photo, pushing the blue and gray wires back into the wall leaves a thin red, thin white (kind of hard to see against the white plastic, but it is over the connection block), thin yellow, and thin green, which are the ones wired like you see in the third photo.

Here's a post from the Jerry's Hurricane Mods thread on the Thor Forum - Very active thread so it took a bit to find it. This is mod to the air conditioner cover to add a standard ceiling AC vent to the cover. Reports from people who have done it are extremely positive.

http://www.thorforums.com/forums/showpost.php?p=71374&postcount=9