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Discussion Starter #1 (Edited)
I need and want a 120V roof AC unit on my well insulated 159WB. There are some install posts here and at Sprinter, but I'd like some ideas on choosing the unit and performance expectations. The 5000btu factory window unit on my 14' RV works great at my highest usage (95F, 80% RH. Typical Roof Airs are mostly 9,200 btu and 13,500 btu. Hein uses a 9.2 on his 170wb Sprinter and likes it. I see that car/truck factory cab units are about 14,000btu. For Coleman-Mach Mach 8 the 13.5K is 3 pounds heavier, costs about $100 more, and uses 1913 watts on full blast vs 1550 for the 9.2K. External dimensions are identical. So choosing one over the other for cost , size, or weight is moot. I want my unit to provide comfort anywhere in US at peak temps and RH. Some here say they just don't work, others say you can hang meat. The Mach 8 Ultra Low units have promise and are readily available. Any input appreciated.
 

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I installed a Mach 1 Power Saver (11K btu I think) so I could power it with my Honda eu2000i generator... it works well but is loud. Next time I'd go with an 8k btu portable model that I could take with me when needed.
 

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I just ordered a camper that offered the option between a Mach 1 power saver and a Mach 8 low profile. The Mach 8 is so loud that it is embarrassing while in the company of others. The Mach 1 power saver is quieter but is a different design so is not low profile which some folks think is desireable.

The Mach 8 now has a "hush kit" available that apparently helps a lot. But that is an extra $140 cost

Links to Discussion about Mach 8 and Mach 1:
https://www.casitaforum.com/invboard/topic/20161-mach-8-displeasure/page__p__188310__hl__displeasure__fromsearch__1#entry188310

More here
https://www.casitaforum.com/invboard/topic/20335-we-went-to-rice-today-to-hear-the-air-conditioner-noise-for-ourselves/page__p__189853__hl__displeasure__fromsearch__1#entry189853
 

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I installed a Mach 1 Power Saver (11K btu I think) so I could power it with my Honda eu2000i generator... it works well but is loud. Next time I'd go with an 8k btu portable model that I could take with me when needed.
Seems to be a popular choice with some manufacturers. The 11,000 BTU/hr Power Saver is rated around 1,000 watts under normal conditions, which is a lot less than the less-efficient 9,200 BTU/hr model. For me it would be a no brainer, although noise doesn't bother me quite as much as it does others. Still, what's really needed is for these A/C guys to offer an energy efficient and quiet roof A/C in the 5,000 to 7,000 BTU/hr size range. Oversizing an A/C so it cycles on and off too frequently isn't good, plus when larger than needed it makes generator size more critical. Or it can't be run as long on batteries like Roadtrek and Hymer do.


By the way, does your Honda 2000 start the 11,000 PS OK, or did you have to modify the A/C to limit start-up current?
 

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By the way, does your Honda 2000 start the 11,000 PS OK, or did you have to modify the A/C to limit start-up current?
Chance,
My original plan was to run my stock Mach 1 PS off my 110v panel powered by my Xantrex Freedom 3012 inverter since the Freedom power center would "automatically" augment the eu2000i... however, Mach 1 static rotor current draw, overhead of the inverter, and Freedom's auto sensing of eu2000i power instability resulted in a strange cycling of power drawn between batteries and generator with no augmentation.

I then rewired to run my Mach1 directly off the shore tie (eu2000i) while limiting my inverter's draw to 10 amps... I added a startup capacitor to the Mach1 to cushion the static rotor draw... and voila, eu2000i easily handles the Mach1 startup (& running). When I run the AC, I set the temp as low as possible so the compressor doesn't cycle on and off... the 10 Amps of current fed to the inverter/charger tops off the house batteries which run everything else. Adding a startup capacitor to the Mach 1 was super simple... it almost looked like they pre-engineered the Mach1 to accept one... hardest part of adding the capacitor was getting the Mach1 cover off/on. I've got pictures of the mod on my www.vancave.wordpress.com website under the "HVAC" page.
Best,
Phranc
 

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Discussion Starter #7
Thanks all. Good tip re Casita forum. An important decision for me is 9.2K btu, 11K, or 13.5K btu. Coleman Mach 8 or Dometic Penguin II? Various posts say a 9.2 won't cut it for hot humid Midwest & SW US. But with a 13.5K I can't plug into a friends garage who has 15A receptacles. Is a 9.2 really inadequate? My experience with 5K in a TT suggest 9.2 would be plenty but many say otherwise but nothing empirical that helps me decide. Does 9.2K in a roof top mean something different than 9.2 for a window unit? Casita owners talk a lot about pre-2016 Mach 8 noise but never say what btu unit they have nor if the unit cools adequately. I'd still like more input cause this is a big investment in effort & $$. With all the various testing there must be some objective data out there.
 

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You have to remember these are small boxes with solid surface walls, floors and ceilings, noise loves this kind of environment. You are how many feet away from the a/c, when in the van. Stand four feet from a 11,000btu window a/c in a small room how much noise is their. Put your thermostat at the opposite end as your a/c to stop short cycling. Is the noise people complaining about, blower or compressor noise. You will have a 100lb unit on the roof that is not design to support that added weight, added support is a must to limit compressor noise. And 9k should be more than enough. Just me thoughts on this.
 

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Thanks much Phranc. I know new Roadtrek and Hymers run A/C off inverter, as do some owners of Sportsmobile. I have to do more research eventually, but believe they run them straight off inverter or generator, not combined. I was aware of that inverter technology, but thought it was mostly intended fo augment shore power, not generator (particularly an inverter generator) because frequency may not be as steady as the massive grid. Again, haven't researched it enough yet to even know what to ask. Thanks again, capacitor information is helpful.





Thanks all. Good tip re Casita forum. An important decision for me is 9.2K btu, 11K, or 13.5K btu. Coleman Mach 8 or Dometic Penguin II? Various posts say a 9.2 won't cut it for hot humid Midwest & SW US. But with a 13.5K I can't plug into a friends garage who has 15A receptacles. Is a 9.2 really inadequate? My experience with 5K in a TT suggest 9.2 would be plenty but many say otherwise but nothing empirical that helps me decide. Does 9.2K in a roof top mean something different than 9.2 for a window unit? Casita owners talk a lot about pre-2016 Mach 8 noise but never say what btu unit they have nor if the unit cools adequately. I'd still like more input cause this is a big investment in effort & $$. With all the various testing there must be some objective data out there.
A/C capacities should be fairly objective in their ratings since they have to follow guidelines -- assuming they don't lie on reports.

What you need to keep in mind when getting random information from the internet is that different users may have different loads that vary far more than the A/C's capacity. For example, a 13,500 isn't but 23% larger than an 11,000 BTU/hr A/C, but total cooling load for two similar trailers may vary more depending on how they are used. Parking in sun versus shade, ambient temperature, humidity, how often they leave door open, whether window shades are used, etc. will impact cooling requirements more than 23%.

I know that my (mostly uninsulated) extended Ford window van cools great at night on 5,000 BTU/hr. During hot sunny day that same 5,000 makes it tolerable in shade, not so much when parked in hot sun (unless I cover windows from outside).

With good insulation, and smaller energy efficient windows, I expect even an 11,000 will keep a large van cool under most reasonable conditions. Having said that, I'm not certain yet I want a roof A/C anyway.
 

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Discussion Starter #10 (Edited)
Phranc,
How do you rate the cooling effectiveness of your 11K unit? How about the roof brace? Would you change that? How useful is the heating strip?

Edit: I just saw your writeup on vancave. Still like to know about the roof brace.
 

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As one data point, on the Casita FBook (very small fiberglass camper) this: Little Mach 8 can't keep up with 95+ temps!


Not sure why anyone would camp in that weather but...
 

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I have a Coleman mach unit that has got to be almost 20 years old that came off a popup camper. It is 9200 btu. Today I ran the ac while working in the van. The window is cracked to run the power cord out, I still haven't insulated my ceiling, my maxxfan vent was open, and we were going in and out of the sliding door all day. The van was parked in full sun. It was a little warm in the van but not bad. I think we were somewhere in the 80's today outside with very high humidity. I left it running for 45 minutes about 8:30 this evening and it was cold in the van. I think the 9200 btu will do exactly as I need.

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Discussion Starter #13
Thanks Josh. This is the kind of info I'm looking for. Sleeping comfort is the driver for me when staying with friends and kin or in a RV Park for a week for a sport event. What amp was your 120v receptacle?
 

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As one data point, on the Casita FBook (very small fiberglass camper) this: Little Mach 8 can't keep up with 95+ temps!


Not sure why anyone would camp in that weather but...

That's funny. When you live in parts of the south 95F days are unfortunately fairly common.

I was just going to mention that the standard rating for RV A/Cs is 95F DB outdoor, and 80F DB indoor. That's the condition used for rating capacity, power consumption, etc.

If you really want hot, they also rate these A/Cs for desert conditions, which is based on 120F DB outdoor and 100F indoor. Short of camping in Death Valley in summer, I'm not sure it has much practical application other than to assure the A/C can survive extreme conditions.



By the way, one of the design features I've heard before about Casitas is that they don't have great insulation. Don't know if that played a role in this one data point, since other factors could also have prevented proper cooling.
 

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We did fine in Florida (highest 92F) with the Coleman Mach 8 Cub/9200 btu's.
So much of how much aircon you need is based on how much insulation eh :)
That and selective parking. In some ways I wish they made an even smaller model.
Lower capacity units would be great, particularly if they could make them significantly smaller and lighter, but that appears unlikely. Physically there isn't that much difference between 9,200, 11,000, 13,500, and 15,000.

Rather than make a much lower capacity model, I'd like to see them add variable frequency drive to reduce capacity as needed rather than have compressor cycle on and off. It's already proven technology in mini split and other residential applications, although it adds cost. Once RV is cooled down running slower would reduce noise, and more importantly, it will make running A/C off batteries at night more feasible when boondocking. A 9,000 to 11,000 BTU/hr A/C could run down below 5,000 at night, which would increase efficiency even higher.

If VFD proves too expensive for RVs, perhaps they can look at other ways to operate more efficiently at reduced capacity -- as presently done on residential A/Cs.

The RV industry just limits options a lot because they try to make most things as cheap as possible, rather than emphasize efficiency a bit more. And that's understandable because RV price-point seems to be what they care most about.
 

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Roblee,
Sorry for the delayed response... I just came back to this thread.

The HVAC brace works great. The 1/8" steel angle with 2x2 wood framing appear to be sufficiently strong when bolted into the ceiling framing... no roof flex or leaks noted to date... although I was careful to mount the wood subframe snug up against the roof panel. I'd build it the same way next time.

11k in my 3500ext is sufficient for muggy southern VA... Mach1PS was able to cool a "hot" van (approx 95F and humid outdoor temps) to 72F in about 90 minutes... air temp was 75 in 15 min but it took a while to cool the interior cabinetry and contents.

Heat strip is worthless.... there appears to be a lot of overhead power draw to power the fan to blow tepid air... I purchased a portable electric 1200w heater which works faster and more efficiently. I also carry a lilBuddy propane heater for realy cold mornings but haven't needed it yet.
 

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I realize this is an older thread, however since I spend time between Orange County, Ca and Lake Havasu City, Az will be 117 today, I'm very interested in learning as much as possible about roof air conditioners since I'm just starting my project... My projects final usage is meant for overnight desert trips to various races with dirt bikes and then a few overnight road bike track-days where asphalt temps can easily reach 115+ in 85 degree weather so a nice place to relax and cool off between races and those long desert weekend trips would be nice.

Has anyone successfully installed and using their a/c unit in hot weather, if so with so many ways to insulate your walls, what method did you use, what did you do for additional roof bracing and what size unit & how effective is it it at keeping your PM cool...

Thanks in advance...
 
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