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Old 07-13-2014, 10:56 AM   #1
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Converting 13.5k ac units to 15k?

A fellow revolution owner and I were wondering about the feasibility of converting our ac rooftop units. Would this appreciably improve cooling and is it plug and play? Would the increase from 13.5 to 15k (as well as brand new units I guess) make a significant enough difference? Or would adding a 3rd unit be more effective?

Chris
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Old 07-13-2014, 11:15 AM   #2
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Chris, here is my humble opinion. I have one of each. It would be hard to tell the difference between the two. My rv has inefficient and restrictive overhead vents. I tried to remove as much resistance inside of them as possible with a small improvement by taking each register out and cutting the protrusion off a bit. The part that goes inside the channels that is. Inside the air conditioners themselves I used some tape to make sure all air was getting to the ducts. My AC covers had small slide registers that would allow air straight down. From experience owning several RV's I have found the ones that vent straight into the RV are far more effective but quite a bit noisier than ones with ceiling registers.

Parking in direct sun in the Sacramento Valley in the Summer makes it almost impossible to cool the coach. Covering windows etc helps and parking East West with the windshield to the East helps but still gets warm inside.

Experimenting for several weeks with modifications I finally closed off the ceiling register conduits and force all of the air out of the AC directly. Cutting out the small slide register part on the AC cover panel was easy and in place is one of those clear plastic register things you would place over your home register vents to force air downward. I now have a huge volume of air you can actually stand under for instant cooling and it keeps the rv much cooler. I took the vent mod a little different way in the bedroom by using a 4 inch pvc pipe with an oblique fitting on the end of a short straight piece. This allows me to direct the air in almost any direction.

The noise level is up of course but the comfort level is way up now.

Critical to the best cooling is cleaning the AC condensers. You may also find some air leaks when you take the outside covers off. Duct tape to the rescue so none of that precious cold air can escape.
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Old 07-14-2014, 04:53 AM   #3
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To convert 13.5k to 15k capacity of BTU you simply install ventilation holes into the shroud at the discharge side of the condenser so more air flow gets across the coil. 1500 BTU's is not much. A third AC unit would be what you need in a real hot environment.
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Old 07-14-2014, 09:38 AM   #4
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I upgraded one unit in a Holiday Rambler. As long as the unit will work with the existing control box, no electrical upgrade is necessary.

Reading specs, the 15k units drew slightly more power. I can't confirm or deny what RV Wizard is saying, other than there may be other differences.

Before going there, I'd recommend pulling the upper cover and cleaning both the evaporator and condenser coils. We find that even with keeping the filters clean, the evaporator coils tend to attract dust.

In hot climates, the best thing you can do is shut down unused registers.. IE - cut off the rear bedroom. I think that the ducted units end up being less efficient, as you're pumping cold air through a relatively warm roof space. I actually thought about un-ducting the front unit of our Holiday Rambler, but never got to it before being sold.
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Old 07-15-2014, 01:52 AM   #5
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My old RV doesn't have any ducts. Maybe that's a good thing!! Air always seems cold in the area it's running.
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Old 07-15-2014, 09:38 AM   #6
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Thank you cb1000rider for that tip. I know that those get dirt in them it never dawned on me I need to clean mine. Duh.

to the original poster. This week we decided to get a lasko UltaAir 48 inch tower fan. price was pretty reasonable and they are ultra quiet. Our bedroom area stays a lot cooler than the rest of the coach due to minima windows compared to the rest of the coach and size. We put the fan by the doorway going into the living area. It is too early to give definitive results but at first trial it seems to be cooler in the living room area. The first day we used it was 100 degrees second was 95. We have an abnormal cool front going on this week so will not be able to see how much it helps but there is still a lot of hot weather ahead in july and august.
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Old 07-15-2014, 12:34 PM   #7
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If I were going to upgrade, I'd be thinking of going to a 17.5 a/c unit... that would be a ~30% increase in cooling capacity and might be worth it... but haven't looked at the details, to be honest.

Steve
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Old 07-15-2014, 01:20 PM   #8
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Hmm... A 17.5k BTU unit. I didn't know they made them that large. Steve, do you have a reference to a roof-type unit?

The only thing I can find is a "midi bus AC unit" - which doesn't look like it comes close to being the same thing.

Does it work on a 20A circuit?


Again - consider: AC rooftop unit, thermostat type, controller, and duct type.

The simplest case is a non-ducted unit with controls that are immediately under the unit and no duct work. The hardest part is getting the new unit on top of the RV (I used a pulley). Expect to spend around $500.
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Old 07-15-2014, 02:51 PM   #9
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My 07 Discovery has two ducted roof ac/heat pumps. I ricently aquired coach with just 20K on her.
Yesterday I pulled BOTH covers, revoved the cover for the evaporator coil/fan and used a can of that AC fin cleaner on BOTH evap & condeser coils. WOW did I see a lot of what looked like a BLACK type of mold or someting on the Evap coils. I used one can each and gave tham a real good cleaning.

I'll post some detailed PICS of the process if others would like to see what's involved. All I needed was a phillips head and some aluminum tape.
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Old 07-15-2014, 03:52 PM   #10
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I've found instead of running air fans on auto put them both on high that way they are not cycling it keeps the coach nice and cool at a constant temp instead of the coach getting hot the air cuts on struggle to cool down then turns off and the cycle starts over.
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Old 07-15-2014, 04:00 PM   #11
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All great ideas y'all, listening. :-)
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Old 07-15-2014, 04:16 PM   #12
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Quote:
Originally Posted by cb1000rider View Post
Hmm... A 17.5k BTU unit. I didn't know they made them that large. Steve, do you have a reference to a roof-type unit?

The only thing I can find is a "midi bus AC unit" - which doesn't look like it comes close to being the same thing.

Does it work on a 20A circuit?


Again - consider: AC rooftop unit, thermostat type, controller, and duct type.

The simplest case is a non-ducted unit with controls that are immediately under the unit and no duct work. The hardest part is getting the new unit on top of the RV (I used a pulley). Expect to spend around $500.
I did see something recently about a larger btu RV AC available. It was not from Dometic or Coleman. I just can't recall the details
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Old 07-15-2014, 04:37 PM   #13
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Quote:
Originally Posted by akeyzoo View Post
A fellow revolution owner and I were wondering about the feasibility of converting our ac rooftop units. Would this appreciably improve cooling and is it plug and play? Would the increase from 13.5 to 15k (as well as brand new units I guess) make a significant enough difference? Or would adding a 3rd unit be more effective?

Chris
Last year I had both of my Dometic 13.5K AC units replaced with 2 new Dometic 15K AC units. The old units were original to my 2006 MH. In addition to the new AC units a new Domestic thermostat was required. Everything else was basically take the old one out put new unit in. Even the original return air ceiling grills were used on the new units. One other thing if your roof top AC covers are painted to match your coach the covers for the new units will most likely be white. I bought some sprayed mixed to match my paint color codes and painted mine.

The new units work great and get the coach cool even here in hot humid Houston Texas.
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Old 07-15-2014, 04:51 PM   #14
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I could have sworn that my parents had a 17.5 on their 5er... but if it is as uncommon as everyone's comments make it seem, I am sure I am wrong. :(

The truth is, I really need a 3rd a/c unit. I wouldn't mind fitting a portable indoor unit with a vent to the outside if I could get someone to do the custom work... of course, it just takes money

Steve
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