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Old 07-13-2015, 10:34 AM   #1
Join Date: Jul 2014
Location: Ohio
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How hard to replace roof a/c units?

Hi, I have a 1999 Dolphin with two original Dometic 13.5 units. I also have the original 4-button thermostat control.

The rear unit has finally given up. The front one appears to be working OK, but cannot keep the whole coach cool, especially here in Nevada right now (104 degrees!!).

I know Dometic uses a phone jack style wire/connector between the units and they are for cooling only as I have a separate furnace. Coach also has ductwork in the ceiling.

I am quite competent working on everything, and I've watched the several videos on youtube on replacing units, sooooo, I was wondering if anyone else had an opinion on how hard it is to replace these units.

I got a couple of quotes and they want, basically, around $3K for everything. I've seen various units online for as little as $550 to around $1200 each.

I think that I would just get new Dometics, 15K units front and back for maximum cooling. Should I stick with using the ducts, or get newer ductless units as I was told that they are more efficient and have less cooling loss?

Anybody know if one Dometic style unit is better than another? For instance, are the low-profile Penguins better than the older style looking Brisk Air2 units?

Also, can I upgrade to the new 12-button thermostat without any issues?

Any advice would be appreciated.

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Old 07-13-2015, 12:31 PM   #2
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You'll have to check compatibility of new units with the old thermostat. If you only replace one A/C, the conflict might be between the new, old, and the thermostat. In that case you'd need a new control board for the old A/C you're planning on keeping. I personally like the ducted units, I think they're quieter and move the air to more locations than the ductless ones.

Removing and replacing the unit on the roof is just a matter of screwdrivers, it's the lifting on and off the roof that might need an assistant.


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Old 07-13-2015, 02:35 PM   #3
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I was just going to replace both units as their both 16+ years old now. I was told that as long as I stay with Dometic I could use the old thermostat by re-setting it by turning the thermostat off, pushing the top and bottom buttons together and holding and then turning it back on. But I thought, new units, new thermostat to go with them.

Other than that it looks to be just unhook power and unplug interface cable, unscrew them, reomve from the roof, get new seal kits with them, set them in place, re-attach power and interface cable, screw them back down and away I'll go.

I will be foil-taping all the joints and parts that I can. I found a red rag stuffed in the one that's still working. Looks like they were trying to keep the exhaust air and intake/cooled air from mixing. Boobs. I hate people that do stuff like that instead of spending a few extra minutes and doing it right.
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Old 07-13-2015, 02:47 PM   #4
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thermostat wiring may be only 4 leads, if so there is a work around for the heat, unless the heaters have their own thermostat.

i replaced our roof top carriers last year with coleman mach HP units. I had to run new 6 strand wiring but that was only becasue the heater wires were in the ceiling
mine came with thermostats, in the box.
might ask your retailer how they ship.
mine came straight from the factory and were boxed different than if my local rv repair center had received them from the local supply wholesaler
plus coleman covered the shipping to my dealer
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Old 07-13-2015, 03:04 PM   #5
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Easy to replace a AC. The easiest way to get it on top is to get a pickup. The taller the better. sit the AC on the bed. Sit a 2X8 across the bed. Get a friend and lift it on to the roof of the motorhome. If it has a rubber roof use thick cardboard or a moving blanket to protect the roof.
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Old 07-13-2015, 03:22 PM   #6
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I agree it is easy to replace rooftop A/C units. The key is the temp control system. We are installing a new Dometic Brisk Air II unit, replacing a 10 year old rear Colman unit. Dometic makes a connection kit between the new Brisk Air II and the old Colman/Intellitec temp system. Have not done the install yet, but the instructions are very clear and straight forward. Believe it will go ok. Have installed a Brisk Air II for the front a/c. Works great. Have a duct system, both units will work well with it.
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Old 07-13-2015, 08:45 PM   #7
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A piece of advice. I do not know if you ever use your MH when it is cooler outside but you might consider a heat pump. I have them on my coach and they keep the coach warm down to around 35 degrees with no problem. Since I am parked in a campground using their electricity I would rather use the heat pumps than the propane for furnaces.
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Old 07-14-2015, 05:34 AM   #8
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X2 on the heat pumps .
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Old 07-14-2015, 08:42 AM   #9
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The coach just has one thermostat that controls everything. The way it was explained to me, wiring goes to the front a/c unit, which then goes to the rear unit and another wire goes from the thermostat to the furnace.

Generally don't camp when it's "cold" out. By the end of October the RV's put away. And my wife like's it like a meat locker in there for sleeping.

The furnace works great and I don't think I'm using more than $5 worth on a weekend, so no big deal. I think I'll call Dometic and see what unit they recommend that'll be the simplest to interface with the wiring I currently have. I guess I can always run new wiring in the ducts, but if they have a setup where I can use the current wiring, all the better.
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Old 07-14-2015, 08:46 AM   #10
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Keep us posted on you progress.
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Old 07-14-2015, 08:53 PM   #11
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I upgraded from the Dometic 4 button to the 5 button Comfort Control with the original A/C's in my 99 Dolphin. With the 5 button or 12 button control you will need to replace the control boxes in the return duct of each A/C. I have electric heating coils in each AC plus the Propane furnace. I got the P/N's for the control boxes from Dometic, searched on line and bought them much cheaper on line including the 5 button control then what Dometic want for them.
Chuck & Teri, 1999 35 ft. Dolphin 5350, F53 Chassis with tag axle, Chassis build date 1/99 in Mexico, Banks System, Trans Command, Air Lift Air Bags on rear, Koni Shocks, Blue OX TruCenter, TigerTrak track bars front and rear, Roadmaster 1-3/4" rear auxiliary sway bar, 2013 VW Passat TDI SEL Premium, 1994 36 ft. Avion 5th Wheel. FMCA #F430129
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Old 07-14-2015, 09:03 PM   #12
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Originally Posted by gemini5362 View Post
A piece of advice. I do not know if you ever use your MH when it is cooler outside but you might consider a heat pump. I have them on my coach and they keep the coach warm down to around 35 degrees with no problem. Since I am parked in a campground using their electricity I would rather use the heat pumps than the propane for furnaces.
Yep, heat pumps for us too even though we have the AquaHot 600 (2 2000 watt elec elements & 50,000 btu diesel), and elec. heated tile floor.
In areas like the Pacific North Wet heat pumps are very well suited to the climate.
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Old 07-14-2015, 09:30 PM   #13
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X3 on the heat pumps....well worth the extra money...
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Old 07-14-2015, 11:04 PM   #14
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I contacted Dometic to see what they recommend. I'll look into the new units with heat pumps and see what the $$ difference is.

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