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Old 07-18-2018, 11:40 AM   #41
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Originally Posted by Kake95 View Post
Where in Cental Ca did you live? I wish it was only 90 in the summer in Cental CA.
I lived in avila beach...and SLO....Gods country, but when I moved to paso the hot and freezing was there... I know that usual temp in the valley were always hotter than avila beach..

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Old 07-18-2018, 12:08 PM   #42
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Originally Posted by Long & Winding road View Post
Great. Let us know your outcome. Hopefully you can get to 45 to 50 deg output temp. If not try leaving your probe loose like another member suggested.

Dont forget to seal or tape the insulation wall that separates the hot from the cold side. Its right in the middle of the AC unit looking straight up. Mine had a few small leaks along the "walls" and could move very easy - so all of the mods add up over time. Others had said it was leaning sideways and leaking major cold air into the warm side so the unit thinks it colder than what it actully is inside the RV.
This sounded like a great "cheap handling fix" for an AC so I decided to go "all in", yank the thermistor out of the fins, and let it dangle.

No difference.

When blowing fan, output temp is 80 deg, and it will drop to 60 deg. within 1 minute when cooling is engaged. I get the same readings whether the thermistor is installed in the fins or not.

My AC is an "Advent" which I got from Etrailer.com to replace my Coleman. Is it possible that the Advent thermistor functions differently on this brand?
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Old 07-18-2018, 12:16 PM   #43
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Originally Posted by Long & Winding road View Post
I thought you were throwing away the rules with me. LOL.

I didnt look at any "splits" or "Deltas" or even "Flux Capacitors". LOL . Im not trying to explain why mine works better Im just telling you what I did to mine and the results I had in hopes it can help others.

All im saying is im getting 18 - 22 degree drop in temperature (from my: uncertified wall thermosat, digtal thermometer in kitchen area and my Auto Zone AC temp probe) consistently.

I don’t know all the fundamentals or have any expertise in HVAC. I don’t have all the answers (I sure wish I did).

All I know is I insulated the cold air return box on the roof, used pipe insulation on the copper tubing on roof and moved my Thermistor probe up about 4 inches and my cold air OUTPUT temp when from 65 deg (at best) last year to 45 degrees (consistanly) this year (with all 3 mods).

It may not work for you but it don’t cost anything to move the probe and its totally reversible so why not try it?

Beside you might find you had a small leak from the cold side over to the warm intake side.

Perhaps with just me fixing my small cold air leak I would have been at 55 degrees last year (which might be normal??) and I only realized a 10 degree again this year.

Why dont we all test our output temps and post hear. (before and after mods) That way we know what the Average norm should be, what the average gain is with diff mods. Just make reference which brand AC you have and BTU output your unit(S) have so we can compare apples to apples.

I think the answer to your 32 degree temp is this two fold:

A: Perhaps the AC stops at "32 deg"... perhaps it stops when it gets to "45" degees? Now See B.

B: Perhaps mine is doing so much better because the ends of the condenser cool quicker (45 deg?) so my unit was sensing it was "cold enough" (it was one inch from the bottom orginally) but now that I moved it up about 4 inches and its in a warmer spot (but unit wants max cool because air is still warm) and now more of the condenser is cooler (Now 32 deg over more coils) so the warm air is getting even colder and it helping drop the output temp?

Maybe? But another post a couple of days ago suggested this was wrong so im just grasping since your looking for answers.

I dont know the answers, I dont even question them anymore.... Im just ejoying the results I have on my unit.

Thow out the "Rules" and just Try it and let us know your outcome.

Im sure in not alone in this. I would love to hear about all the temps and the tricks that we all have for the AC system.

Enjoy the cool breeze and think of of the poor soles without RVs to tinker with.
thanks for the detailed reply,as you have seen I have done an extensive mod to my ac, and like you mentioned the divider wall leaks into the return, on mine the wall was mismatched by 1'' I completely re did the stock grille and went with a residential grille..I pulled the probe as suggested here,
not any difference as the ambient temp in vegas was over 120 degrees..I think the 15,000 btu ac Is about 1.2 tons..that would be enough to cool close to 500 sq. ft. is it had correct R value construction..but with all the single pane glass, and all the low R walls, you are tring to cool the outside temp....not gonna happen...So, last night, with the rv plugged in, I set the stat to 70 degrees … this morning, the unit was off in cycle mode as I set the stat to auto... freexing cold in side ..my temp gun showed 63 deg. on the counters..67 on the pillows in the bed room...but,... un like my always rule... I changed too many thing, years of racing dragsters taught me to make a pass after each change to know if the change went in the right direction..
.I doubled the size of my return air, and doubled the size of the service grilles in the front end of my coach...my coach has 8 little round vents and after removing them ( the grilles) it worked better, and I could see where they cut 2 more in after the fact because they used a hammer and screw driver to cut in 2 more holes in the bedroom

it's my belief that the ducts and vents are too small for the size of the ac unit, so, even though it's a 15,000 btu,.. you're probley getting the efficiency of about 12,000 at best , now with the mods so far, the coach has even cooling through out,.. I put a metal plate on the cool side and tossed the stock grille.. the ducts being too small caused too much restriction
so I drilled 3 1 1/4 holes in the plate, even after cutting the 3 hole I still had the same volume at the vents and the unit got quieter … I think I'm pretty much there for in the shade...and at 100 degree temps..on the list is window tint, glare strip on windshield, and the roof mod you did... I just can't under stand why the condenser fan sucks the air into the unit??? that just heats the compressor and duct work and in fishing this long drawn out post... thanks for all your input..
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Old 07-18-2018, 12:20 PM   #44
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Originally Posted by DonKarstedt View Post
This sounded like a great "cheap handling fix" for an AC so I decided to go "all in", yank the thermistor out of the fins, and let it dangle.

No difference.

When blowing fan, output temp is 80 deg, and it will drop to 60 deg. within 1 minute when cooling is engaged. I get the same readings whether the thermistor is installed in the fins or not.

My AC is an "Advent" which I got from Etrailers.com to replace my Coleman. Is it possible that the Advent thermistor functions differently on this brand?
I got the same results, I don't "THINK" the probe will do anything when it's over 100 degrees out side...I did get 47 deg. coming out after the unit ran all night , I did cycle off and was off when I got up this morning,,so I lowered the stat to 65... that's when I seen the 47 deg..
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Old 07-18-2018, 12:26 PM   #45
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Vegasruv24.1- I got your PM but was preoccupied today.

I like what you first said here, being willing to throw out something you thought you knew to learn something else is the sign of a smart person. I know I've had a whole pile of things I THOUGHT were one way, only to learn they were another. It pays to have an open mind, that's for sure.

So the biggest thing I can say is I THINK the thermistor isn't letting it get anywhere near 32 degrees. That's the key here. This is what I mentioned earlier here...


What if they were cycling back the compressor at temps that are way higher than 32 degrees? H#ll, I don't even know if these compressors are variable displacement, expansion valve or orifice tube systems. I never got that far into bothering to find out more about the compressors themselves. Anyway they do it, they clearly have evaporator icing feedback because they have a thermistor. So they can be as aggressive or as conservative as they want with those strategies. What I did by removing the thermistor from the evap core was basically being as aggressive as you can be on the compromise between low output temps and chance of icing.

I do know this... Coleman has to be SUPER conservative on their units because the same design/calibrations have to work "OK" on hundreds of different applications. It's very similar to what I said in the 5 Star tuning thread, the way Ford has to be VERY conservative on how they calibrate the engine operation on an engine that has to be used in hundreds of different situations and conditions.

This is important because it means there's the strong possibility of major improvements in efficiency in your (ours, or anyone else's) particular situation. If Coleman makes an RV roof air that they absolutely don't want to ice up because it would result in bad customer experiences, they have to make sure it won't ice up in the worst possible situations. I personally want the compromise to be maximum cooling and would simply avoid the "worst possible situations". Like closing all the vents or leaving the AC run all night, or running it non-stop when it's not that hot out.

BTW where did you come up with a "22 degree split" being the "very most efficient"? Just curious. I've had aftermarket dash AC's in cars and motorhomes that would turn the evap core into a giant ice cube in 100+ degree weather. Easily putting out 30 or even 40 degree temp drops from inlet to outlet.

If I get bored, I'll get you guys some actual real data. I can monitor the AC amp draw in my Vegas. All I have to do is put the thermistor in a glass of water and see at what temp the compressor cycles or changes displacement. I'd start with ice water, moving up the temp to find out EXACTLY how cold they let the evaporator core get. Or you guys can just be crazy and try what I suggested. Just pull the thermistor out of the evap core and see what happens. Sometimes you just have to throw theory and debate out and experiment blindly.
make sense as the unit will last way more longer if it cycles off at 45 deg,. instead of 32 deg,.. and thanks for posting... my struggle right now is not the unit anymore, but try'n to get the heat out and the cool in...
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Old 07-18-2018, 12:27 PM   #46
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first off... I am willing to throw everything I know, or think I know out the window to learn something new....the probe deal...seems to me that it is a temp sensor that senses 32 degrees and shuts the compressor down..... sound about right???? and the AC is a cold / heat exchanger.... right... meaning the Freon comes in to the evap cold, the warm air inside blows across the evap and cools and blows out the service duct... the hot Freon goes then to the condenser...where it is cooled... then back to get re compressed, making it cold again... sound about right???? so the probe does nothing till the evap gets to 32 degrees.... right???so would you mind giving more imput that I obviously don't have....how would moving the probe up or down do any thing, unless you were freezing up the coils???next,... the very most efficient...is a 22 degree split.... your say'n that you are getting a 27 degree split... but @ 90 degree ambient temp, 72 is only a 18 degree temp drop...
I haven’t read through all the posts, but doubt this has been covered. First, since you are willing to learn and I have experience designing and installing large refrigeration systems, I’ll add that your order of equipment the refrigerant goes through isn’t correct. For the context of this thread, however, I don’t think that matters much. Just mentioning it in case you want to look it up or discuss it further.

Secondly, you should think of the evaporator as a heat exchanger that is designed to operate with as little refrigerant pressure drop as practical. This means that in an evaporator, refrigerant goes in mostly as liquid and “evaporates” from liquid to gas at essentially (plus or minus) one pressure and thus one temperature. As long as there is a mixture of refrigerant liquid and gas present, the temperature won’t be significantly different. It’s only after all liquid has evaporated that the remaining refrigerant gas will warm quickly and not cool as much.
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Old 07-18-2018, 12:40 PM   #47
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here's my almost done duct remodel...still have to paint the screws white... but I did find this, the ceiling is some sort of man made stuff, kinda like pressed foam,... thor used hex head self taping screws to mount the grilles… most were stripped and fell out when I removed the grilles, that and a vacume load of debris blew out .. I installed mine with mollies and was able to turn the screws to tight..
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Old 07-18-2018, 12:44 PM   #48
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I haven’t read through all the posts, but doubt this has been covered. First, since you are willing to learn and I have experience designing and installing large refrigeration systems, I’ll add that your order of equipment the refrigerant goes through isn’t correct. For the context of this thread, however, I don’t think that matters much. Just mentioning it in case you want to look it up or discuss it further.

Secondly, you should think of the evaporator as a heat exchanger that is designed to operate with as little refrigerant pressure drop as practical. This means that in an evaporator, refrigerant goes in mostly as liquid and “evaporates” from liquid to gas at essentially (plus or minus) one pressure and thus one temperature. As long as there is a mixture of refrigerant liquid and gas present, the temperature won’t be significantly different. It’s only after all liquid has evaporated that the remaining refrigerant gas will warm quickly and not cool as much.
I no doubt didn't word my post right, nor did I get to exact detail...but agree with your post..thanks for posting..
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Old 07-18-2018, 12:50 PM   #49
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I haven’t read through all the posts, but doubt this has been covered. First, since you are willing to learn and I have experience designing and installing large refrigeration systems, I’ll add that your order of equipment the refrigerant goes through isn’t correct. For the context of this thread, however, I don’t think that matters much. Just mentioning it in case you want to look it up or discuss it further.

Secondly, you should think of the evaporator as a heat exchanger that is designed to operate with as little refrigerant pressure drop as practical. This means that in an evaporator, refrigerant goes in mostly as liquid and “evaporates” from liquid to gas at essentially (plus or minus) one pressure and thus one temperature. As long as there is a mixture of refrigerant liquid and gas present, the temperature won’t be significantly different. It’s only after all liquid has evaporated that the remaining refrigerant gas will warm quickly and not cool as much.
what I post was the reference to ac/heat pump...just a reverse of the process..so the same unit will cool … or heat when it's 120 deg ambient, it will work way more efficient in heat mode..right?..
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Old 07-18-2018, 12:53 PM   #50
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Wow, looks nice.
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Old 07-18-2018, 01:11 PM   #51
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So it looks like there is 3 (or more) ways to "help" our AC units cool better.

1. Do what I did - move probe up a few inches then test, move again then test. Plus insulate box and pipes on top as well as check for leaks inside.

2. Remove probe entirely and let it dangle down (but I think I would still insulate the box/pipe + check for leaks).

3. Block off the cold air dump under unit to force air though vents in ceiling (But I would add 2 - 4 more small round vents if it was me) and enlarge the cold air return. Plus insulate box and pipes/check for air leaks.

Or try all 3 and let us know the outcome of each.
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Old 07-18-2018, 01:15 PM   #52
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VegasRUV24.1 - I like the idea of "making my unit quieter". That would motivate me to try your cold air return idea.

I thought about using some thin cold air return insulation (the kinda that absorbs sound) and installing on boths sides (Hot and cold). I bet that would help some.
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Old 07-18-2018, 04:37 PM   #53
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The whole idea of moving the probe or thermistor hinges on what system they have in these units. Like I said, I honestly don't know and didn't look. If you guys want to know FOR SURE how the probe works, do some research or do some actual scientific testing. Pulling or moving the probe and saying "it made no difference" means nothing.

First thing to do is find out how the system works. Is it a CCOT (cycling clutch orifice tube) system? Is it a capillary tube/expansion valve system? Is it a variable displacement compressor? (clutch or power doesn't cycle, it simply changes the stroke of the compressor.) What exactly does the anti-icing strategy do, does it turn off the compressor electrically, change the output or change the orifice of an expansion valve? I Personally have no idea because all I did on mine was pull the probe for now (too many other projects to dive into this one right now). Mine hasn't frozen up and outlet temps are cooler as per my temp gun looking at it ONE TIME.

Second thing or idea is like I said, pull the temp probe. Put it in a glass of ice water. What happens to the output temps? What happens to the compressor? What do the high side and low side tubes feel like? (HUGE diagnostic tool when dealing with AC systems btw.) What are the actual evaporator AND condenser temps? What is the amperage change?

The big question that is still unanswered is this... IS THE TEMP PROBE AN ON-OFF INPUT OR SLIDING/VARIABLE INPUT? We don't even know that. If it's an on-off input (or output from the control box), at what temp is it switching. Another unknown.

Too many unknowns if you guys want to have real answers. That's why I suggested two routes, simply pull the probe and give it some time before you make an assumption on what effect it had. Or go about it scientifically and first understand the exact system operation, then get actual data. I'm sorry I can't dive into this further right now other than throwing ideas out there. We're taking the boat to the lake this weekend, maybe I'll have a chance to get a little data for you all. I know it's going to be hot. Not Paso Robles hot btw, haha! F that. My father in law lives in Atascadero. We joke that it's not "Gods Country" but more like "Satans Country" because of the super hot summers and super cold (relatively for California) winters.
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Old 07-18-2018, 04:38 PM   #54
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I see frost king has different thickness insulation. Did you use the 2" pictured. Looking at the pics you posted it doesnt look 2" or is it just compressed down.

And it looks like you only covered the one copper pipe with insulation. Im assuming the other pipe pictured doesnt need covering

Jerry
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Yes, Aluminum tape and Frost King Duct insulation (which is self adhesive). But under all that I used some left over Fat Mat (the thiner kind like Dynomat) on the top and the front sloped side only - not sure If I would do the entire box with Fat Mat for the cost to benifit ratio.

Plus I used zip ties on the pipe insulation since over time I was afraid the small self adhesive strip will let go and I dont want it to get caught up in the fan blades.
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Old 07-18-2018, 05:53 PM   #55
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I see frost king has different thickness insulation. Did you use the 2" pictured. Looking at the pics you posted it doesnt look 2" or is it just compressed down.

And it looks like you only covered the one copper pipe with insulation. Im assuming the other pipe pictured doesnt need covering

Jerry

I used the self stick frost king and its only like 1/2 thick at most. Im sure you can use the other one but not sure how well it would hang on with the heat on the roof. But I also put some thin Fat Mat (just like Dynomat) on the top and the front sloped side as well so its almost double insulated.

I thought about doubling up on the Frost king but I figured I would benifit most by having the foil outiside part relected the heat so the 2nd layer may not do that much plus I was not sure if I could get the plastic lid back on when done.

Yes the pipes I covered was the only "cold ones" that I felt when testing.

I might crank up the unit this weeknd and touch the cold air box (the parts I insulated) to see if it feels cool or hot or normal then I will see if another layer will fit under the cover.
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Old 07-18-2018, 05:57 PM   #56
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I see frost king has different thickness insulation. Did you use the 2" pictured. Looking at the pics you posted it doesnt look 2" or is it just compressed down.

And it looks like you only covered the one copper pipe with insulation. Im assuming the other pipe pictured doesnt need covering

Jerry
I feel like im in "Ground Hog Day".... I just answered this same question on the other tread just now. LOL.

Its like 1/2 inch thick. Not sure if enough room to go double thick but it might (will look this weekend). I only insualted the pipe that was cold to the touch.
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Old 07-18-2018, 09:07 PM   #57
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I think you missed part of the point about the delta T.

if you start off the day to do your mods, and it's let's say 90 degrees F inside.
So a properly running unit will be pushing out air around about 70-75 after it's running for a few minutes.
So you start messing around for an hour...taping things up, moving probes around, taking measurements.... the whole while that air conditioner is bringing the inside temp down from 90 to let's say 80 now.

Now, assuming the AC is still running at the same efficiency...but it's now starting with 80 degree air rather than the 90 before.
so 80-15= 65...so now it's output is 60-65.

Did your improvements make for a 10 degree improvement?

nope, no change at all.

The thing is only capable of so much energy transfer and is only so efficient. No doubt improvements can be made...and you've suggested some things that make sense...but at the end of the day it's taking in air and can only drop the temp of that air so much. It's how much it's dropping it that is what will tell you how well your improvements work.... the difference, or delta T... the outlet temps are only part of the equation....
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Old 07-18-2018, 09:20 PM   #58
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I think you missed part of the point about the delta T.

if you start off the day to do your mods, and it's let's say 90 degrees F inside.
So a properly running unit will be pushing out air around about 70-75 after it's running for a few minutes.
So you start messing around for an hour...taping things up, moving probes around, taking measurements.... the whole while that air conditioner is bringing the inside temp down from 90 to let's say 80 now.

Now, assuming the AC is still running at the same efficiency...but it's now starting with 80 degree air rather than the 90 before.
so 80-15= 65...so now it's output is 60-65.

Did your improvements make for a 10 degree improvement?

nope, no change at all.

The thing is only capable of so much energy transfer and is only so efficient. No doubt improvements can be made...and you've suggested some things that make sense...but at the end of the day it's taking in air and can only drop the temp of that air so much. It's how much it's dropping it that is what will tell you how well your improvements work.... the difference, or delta T... the outlet temps are only part of the equation....
Your right but I always test the next day and note the outside and inside temps when I start so I can compare apples to apples.

But keep in mind that most of us have been using our RV's for a while so any mod we make we know its working if its drastic. Dont take a Rocket scientist to know that 45 degree output temp is better than 55 or 65 and WILL cool the rig sooner and should yeild lower inside temps over time.

Last year the best I could do was 82 deg in full sun with refective bubble at 95 deg outside temp. This year NO bubbles (but tinted windows - but the bubble would insulated much better) 95 degrees at the same house facing the same direction and I can get 72 - 74 deg. consistantly.
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Old 07-18-2018, 10:21 PM   #59
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.....cut...

The thing is only capable of so much energy transfer and is only so efficient. No doubt improvements can be made...and you've suggested some things that make sense...but at the end of the day it's taking in air and can only drop the temp of that air so much. It's how much it's dropping it that is what will tell you how well your improvements work.... the difference, or delta T... the outlet temps are only part of the equation....
A significant portion of the A/C’s rated capacity is used to remove moisture from the air. You’re correct that measuring temperatures alone doesn’t tell the entire story. When tested for certification, these A/Cs are operated under controlled conditions which includes relative humidity.

One thing that is a CERTAINTY is that when A/Cs are operated at lower evaporator pressure/temperature, they will require more power per amount of cooling; assuming everything else remains the same. The compressor has to elevate the refrigerant from a lower pressure up to the condensing pressure. That means lower A/C thermodynamic efficiency. You also lose overall cooling capacity.
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Old 07-18-2018, 11:17 PM   #60
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I can't help but notice there is somebody on here who sounds like an engineer who is so obsessed with thinking in black and white that he's paralyzed from making any discoveries that haven't already been documented and proven. Hmmm, maybe that's why he's also paralyzed by fear of not buying the "perfect" RV? Perfection does not exist. The world is not black and white. Thankfully there are many shades of grey in most everything.

That's not the kind of people that made this country and world as advanced as it is today. I live a few blocks from where Steve Job's old house was. Where would we all be if somebody told him "Telephones are for talking on and are most efficient when used in that manner. Don't bother trying to modify a phone into something it wasn't designed to be." Lol.

Case in point, Funny Car engines aren't very efficient. They're pushed WELL beyond what an internal combustion engine was originally designed to do. The reason we have 10,000hp Funny Car engines is because somebody (actually a whole lot of somebodies) didn't accept the idea that efficiency can't be changed.

Think outside of the box. It's amazing what you might learn. It could possibly be something that could change the world. If all you know is what's already been figured out, you cease to evolve.
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