https://pdfs.semanticscholar.org/ea3...8748bbe044.pdf
I really like reading tests like this, you can learn a ton from them. For those that don't like reading technical gobbly gook like this, here's a quote from the conclusion...
This little quote could explain why a lot of you had older coaches that cooled fine, but now have similar sized newer coaches that don't.
So I stand corrected on a comment I made about these RV roof air conditioners not changing much in the last 3 or 4 decades. I was wrong. They got LESS EFFICIENT, mostly in very hot conditions. I don't know about you guys, but I usually want my AC to work at it's best when it's really hot. lol. When we need these roof AC's to work is when it's super hot and there's a ton of heat load. That's when people are complaining about their AC performance. The surface temps on the deck of my boat on that 100 degree day were as high as 165 degrees. I didn't go up on the roof of my RV, but I'm betting the temps in that roof air unit were well above that. I'm willing to bet the compressor temps were easily nearing 200 degrees, if not over. High and low side pressures are ~ 500psi/250psi on these 410a systems, which is insanely high. Automotive R12 and R134a systems generally run high and low pressures around 175psi/35psi. High pressures create high heat. That heat has to be dealt with in order for the AC system to properly cool the inside air.
Wanna talk about heat loads? Somebody needs to calculate the BTU's created by these generators running under the coach and the inefficient roof air conditioner compressors pumping out tons of heat simply to build these high pressures (not even mentioning the actual heat extraction process). The whole process is WILDELY INEFFICIENT. You have a generator turning mechanical energy into electrical energy. Then you have a roof air turning that electrical energy back into mechanical energy. (Twice actually, one being the compressor and the second being the fans.)
Think about this as an alternative, IF the RV equipment manufacturers cared to invest R&D money into this stuff... The generator could easily directly drive an AC compressor AND fan system for the air distribution mechanically, skipping the entire mechanical/electrical/electrical/mechanical conversions and their inherent losses.
That scenario would be the ultimate in efficiency. The next level would be something like the residential split systems. (I'm still seriously considering grafting a mini-split system into my Vegas BTW.) They are FAR more efficient than what companies like Coleman and Dometic are putting out for the RV community. The next level would be what RV roof AC systems USED to be, with a refrigerant that worked better when you really need it, when temps are very high. (Obviously that's not possible, those "bad" refrigerants are gone. Just stating it because it's a level that was above what we now have.) The very last level of efficiency... What we have on our newer coaches. It's cr@p.
Yes, everything you guys have mentioned about the actual heat loads of the RV are valid. Yes, it's a major factor. But the bottom line, IMHO, is that these roof AC units aren't even close to as efficient and strong as they easily could be.
BTW, as far as my particular RV's heat loads go, I've got more insulation in mine than you guys do, I can guaranty that. Somebody mentioned the front cap being empty behind it. Yeah, If you guys have been keeping up with my mods, I GUTTED THE ENTIRE CAB of my Vegas and insulated all of that stuff. I even gutted the rear cap, which also has NO insulation, and insulated it. I've got literally thousands of dollars in insulation and sound deadening in my Vegas. If mine's getting hot, a stock one would be getting inferno hot. lol. That 99 degree reading on my inside temp picture I posted? You can bet that number would be significantly higher on a bone stock Vegas or similar coach. Mine's not stock.
Here's some pics of my Coleman 15k for you guys. So much of what I see here makes me just shake my head. Like the squirrel cage fan and how the area it's in is designed. WTF??? Just plain inefficient/old/poor design and cheap components.
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