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Ramblin John · 02-17-2019, 04:05 PM

Has anyone installed a third roof AC without a factory frame in place?

Oregonpharme · 02-17-2019, 08:55 PM

I did on a large fifth wheel about thirty years ago. I swore I would never do so again after that experience. Here is what I discovered: The new AC must be located near a roof joist to support the weight. The hole that is cut must be framed between the upper roof and the inside ceiling, and fastened to the joist with solid wood framing to hold the vibrating mass, and keep the roof from compressing when the AC is mounted and the mounting bolts torqued down. The 120 VAC wiring must be run inside the roof, then through the new wood frame to power the AC - much easier said than done, as you need to run from the commercial power breaker system up through the wall and then through the roof insulation to the new AC. You need about 20 amps of breaker for each AC unit, that means a minimum 50 AMP service and an independent breaker for the new AC (and addition of capacitor start system if all three units are operating). If I were thinking of such a project again, I would simply go buy two new 15,000 BTU AC units and replace the lower rated old ones.

nodine · 02-18-2019, 04:25 AM

Quote:

Originally Posted by Ramblin John

Has anyone installed a third roof AC without a factory frame in place?

I have considered that from time to time and would use the factory opening for the Fantastic Fan. That opening is the same as the one used for the roof airs. One of the mods I have made to our coach is to add two additional outlets, one in the bathroom and one in the hall. These are fed from the pedestal 20 amp or 30 amp outlet by using a custom cord that plugs into a 20 amp connector in one of the bays. The location of these outlets and the routing of the romex leads me to believe that I could fish a circuit from the hall outlet up to the ceiling area to feed that extra roof unit. I would use a standalone roof unit with the thermostat and controls an integral part of the unit. Coleman makes a 9000 BTU unit like this for small campers that would be perfect for this type of mod. I would only use the unit during very hot weather when the other two units need a little help. Of course this approach is particular to my application and your situation may be quite different. Just giving you some food for thought.

https://www.rvupgradestore.com/Mach-...Us-p/63840.htm

Here is a larger unit.
https://www.amazon.com/Coleman-48203...ir+conditioner

https://www.amazon.com/Coleman-9430D...T0X39C7459WMBD

Bob

RustyTools · 02-18-2019, 05:00 AM

Yes, on my '06 Endeavor Atrium (as the name says, the slideout had lots of windows all around so it got hot).

I used the center vent where the fan was. I talked to Monaco Engineering folks (RIP) before I started and they said they couldn't authorize a DIY job, but indicated some other models already had the 3rd unit. The hole was already framed in aluminum - no wood up there except for maybe trim. No major issues at all, except that when lifting it to roof I found AC units got heavier as I get older

. I installed a new breaker and a switch so that I could run the center air off either existing wiring or from a separate 12 ga line.

The 8kw QD Onan did fine with all 3 running too, altho i was pretty close to max capacity - and made sure no other appliances were on. And tried to stagger thermostat settings so they wouldn't all try to kick in simultaneously. I used existing thermostat unit too.

I'm considering doing it to my Camelot.

Should be some threads on the project several years back. Good luck!

RustyTools · 02-18-2019, 05:07 AM

Bring the parts next week, Bob, and I'll bring the chainsaw.

Ivylog · 02-18-2019, 06:56 AM

No way would I cut a hole in the roof of a 2018 MH. I could not find which ACs you have??? If 13K I would replace one with a 15k (or both) as two ACs should cool your 39’ MH.

Ivylog · 02-18-2019, 06:57 AM

No way would I cut a hole in the roof of a 2018 MH. I could not find which ACs you have??? If 13K I would replace one with a 15k (or both) as two ACs should cool your 39’ MH.