We're doing a major renovation of our 10 year old National MH this year, (roof work, slide seals and paint) and I'm thinking about replacing both Duo-Therm A/C units only because they are 10 years old. Both still work fine but as any electro-mechanical devices exposed to the elements, they have a limited lifetime and repairs/replacements on the road are generally more expensive.I may even replace one 10k BTU unit with a larger (15K BTU) one. Are there better units available?...better brands, newer technology?I'd like to be able to use the same controller which also controls the furnaces etc.

You have the lcd CCC system so you will have to stick with DometicYou do NOT have a 10k. you either have a 11k in the bedroom and a 13.5k up front or 2 13.5k units. Doug

Although I understand your argument that replacements on the road may be difficult, what are the odds that both units go out at the same time? Your unit has ducted air right? I have the same year National RV as you and both my units still work fine. I wouldn't even consider just replacing them just for the sake of age. When they go out I'll replace them. It's not like only running on one AC unit creates an emergency or leaves you stranded.Sorry, I realize that doesn't answer your question, but I was just having trouble understanding the logic.

I am not a member of the throw away generation, and this is one prime example why. Those AC units will, in all probability last another 10 years and provide good service. Why would anyone toss $2000 in the trash, just because they "might" break somewhere down the road? Sorry, but I can NOT agree with your reasoning. I have been RVing since 1974 and have not seen to many AC units go south at 10 years of age.....

Seems the new units are using r410. They also claim to be more efficient, but based on the spec sheets, don't see a lot of difference. I just ordered a brisk air 2 with 410 in it to install as a third unit. Some places I go the 2 won't keep the temp where I want it. To me if you spend time in hot areas you can't have enough a/c. So I would buy the biggest units you can afford.Wherever you buy the units from should be able to tell you if it will work with your controller.

If they are working efficiently I would leave them be. When the day comes when one fails the hardest part of the replacement if getting the new on the roof and the old one down. Going with higher BTU units is difficult to judge. If you have too much cooling capacity you will lose the dehumidifying effect and the coach will feel like a cave. Cold and damp. If you do replace them consider going with heat pumps if your camping habits will support the use and additional cost. Spring and fall are my favorite camping times but keeping a supply of propane for heat is something I would like to do without.The original thermostat should work. More or less it's no more than a dry contact relay that will command the unit to turn on and off. If you do replacement just to be sure contact the manufacture.As part of the refurb project I would consider looking to see if you can add drain lines somehow rather than the condensate draining on the roof.

Replacing Roof Top A/C units | Good Sam Community

dougrainer
Nomad
Jun 25, 2013
jmaddy wrote:
I cannot locate my AC manual for my 1999 M-6350 National RV. Which brand will replace my existing units? I don't want to modify the existing hole in the roof. Does anyone know what the roof hole size is on the 6350?

Thank You in advance.

ALL National Products and ALL RV's have the same size hole for a RV roof top AC unit (14 inch square). Your AC units are made by Dometic. National always used Dometic. 1999 means you have the Dometic wall CCC 4 button tstat control system that uses a telephone type cable top communicate between the 2 roof AC units and the wall tstat. That system was obsolete in 2001. That means the easiest and simplest thing to do is purchase new Dometic AC units and I would get the Penguin Model, because THAT model has the new AC tstat control boards already installed. You only have to purchase the new 12 button Dometic wall tstat. The 1 tstat controls BOTH AC units. Just like your present Wall tstat. Doug
jmaddy
Explorer
Jun 24, 2013
I cannot locate my AC manual for my 1999 M-6350 National RV. Which brand will replace my existing units? I don't want to modify the existing hole in the roof. Does anyone know what the roof hole size is on the 6350?

Thank You in advance.
msmith1199
Explorer II
Jun 17, 2013
The Texan wrote:
msmith1199 wrote:
The Texan wrote:
Why not replace the roof with a solid type, instead of another rubber roof that is subject to the same problems you are correcting? There are multiple companies that do this and everyone I know that has had it done is super happy with the results. It is similar to LineX or Rhino. One such company is RV Roof.com in Florida, but there are others.

Almost $5,000 for a 35 foot motorhome? Quite expensive.
Just used that website as a demo of what can be done with the roof type spray on hard liners. There are others and the prevailing prices that friends have paid, have been UNDER $3000 for a complete job.

$3k may be more reasonable. I have a one piece fiberglass roof on my motorhome and the only places I've had issues have been at the seams and around the skylight over the shower. I wonder if it would help any (and be a lot cheaper) just to put this stuff over the seams in the front and back and around the other problem areas, instead of coating the entire roof.
Ozlander
Explorer
Jun 13, 2013
msmith1199 wrote:
Then what else should be replaced on the RV that is still working, just in case it fails? Fridge? Heaters? Water Heater? Engine? Tranny? Tires? Okay, I did do the tires based on age and not tread wear, but that's a big safety issue.

And the rear end.

The only thing you gain by replacing the AC's is a two year warranty.
The_Texan
Explorer
Jun 13, 2013
msmith1199 wrote:
The Texan wrote:
Why not replace the roof with a solid type, instead of another rubber roof that is subject to the same problems you are correcting? There are multiple companies that do this and everyone I know that has had it done is super happy with the results. It is similar to LineX or Rhino. One such company is RV Roof.com in Florida, but there are others.

Almost $5,000 for a 35 foot motorhome? Quite expensive.
Just used that website as a demo of what can be done with the roof type spray on hard liners. There are others and the prevailing prices that friends have paid, have been UNDER $3000 for a complete job.
msmith1199
Explorer II
Jun 13, 2013
The Texan wrote:
Why not replace the roof with a solid type, instead of another rubber roof that is subject to the same problems you are correcting? There are multiple companies that do this and everyone I know that has had it done is super happy with the results. It is similar to LineX or Rhino. One such company is RV Roof.com in Florida, but there are others.

Almost $5,000 for a 35 foot motorhome? Quite expensive.
The_Texan
Explorer
Jun 13, 2013
Why not replace the roof with a solid type, instead of another rubber roof that is subject to the same problems you are correcting? There are multiple companies that do this and everyone I know that has had it done is super happy with the results. It is similar to LineX or Rhino. One such company is RV Roof.com in Florida, but there are others.
subtroll
Explorer
Jun 13, 2013
I appreciate all the sentiments and comments. Thank you.

I had two more reasons for thinking about replacing the units. The first is we plan a major upgrade to the roof soon to replace a couple of patches, remove two inoperative solar panels, remove many feet of sealing tape, replace a bathroon vent with a second Fantastic vent and add a new white EDM roof. When the new roof is in place, I'd like to stay off the roof the next few years.

In addition when we paint the entire coach this fall, the A/C covers will be painted a matching color, ie why not paint new covers rather than later end up with a mismatched set.

We're enjoying our tenth season in this National MH after starting in 2004 with zero warranty items and nearly trouble free 110k miles in all states (except Hawaii) and all Canadian provinces. By renovating the roof, replacing slide seals and a new paint scheme it will be a new coach to us and should keep us on the road a few more years.
Jarlaxle
Explorer II
Jun 13, 2013
Both A/C units (one Dometic, one Coleman) in my bus are 15+ years old...both work perfectly. Roof airs last a LONG time. The one in my friend's 1974 Dodge class C is original!
B_s_Bunch
Explorer
Jun 13, 2013
the front ac went out on our previous coach. Had the five year extended warranty. JUST PAST THIS DEADLINE. I replaced both. Got my money back when we traded or so the paper work says??? Didnt do it for trade but we managed to trade soon after replacement. Im happy and I am sure the new owners are also. I try to take care of my equipment. Larry

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