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Old 06-15-2021, 04:55 PM   #1
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Question Power Source for Existing A/C

I want to keep my existing AC unit, but I'd love to be able to run it when the engine isn't running. What are my options? Can I patch in a different power source? I'm assuming of course that it will have to be straight from a battery bank or generator, but I'm unclear whether it's even possible. Any advice is welcome.


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Old 06-15-2021, 05:20 PM   #2
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https://www.skoolie.net/forums/f49/r...tml#post442413

Funny timing...there is literally the same discussion happening in that thread. I think this other question was also posed today. Was there a blog post or YouTube video launched today that mentioned this?
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Old 06-15-2021, 05:48 PM   #3
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my advice is that unless you are well versed in Mobile A/C and also mechanics / engineering then keep your existing A/C for the road and install another system for when you are parked..
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Old 06-15-2021, 05:50 PM   #4
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Quote:
Originally Posted by rossvtaylor View Post
https://www.skoolie.net/forums/f49/r...tml#post442413

Funny timing...there is literally the same discussion happening in that thread. I think this other question was also posed today. Was there a blog post or YouTube video launched today that mentioned this?

maybe they read my thread on "dont rip out your factory A/C"..
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Old 06-15-2021, 06:00 PM   #5
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Originally Posted by cadillackid View Post
maybe they read my thread on "dont rip out your factory A/C"..
A great thread...but that's been around for a while. It just seemed odd that two new members would ask the same obscure (but creative) question on the same day.

Your A/C thread should be required reading, though.
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Old 06-15-2021, 06:27 PM   #6
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Quote:
Originally Posted by cadillackid View Post
my advice is that unless you are well versed in Mobile A/C and also mechanics / engineering then keep your existing A/C for the road and install another system for when you are parked..
Thank you! I agree, this is likely what we will do. Considering a roof unit for when we're parked, and existing system for when we're running.
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Old 06-15-2021, 06:28 PM   #7
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maybe they read my thread on "dont rip out your factory A/C"..
We totally did read this lmao
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Old 06-15-2021, 06:28 PM   #8
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Quote:
Originally Posted by rossvtaylor View Post
A great thread...but that's been around for a while. It just seemed odd that two new members would ask the same obscure (but creative) question on the same day.

Your A/C thread should be required reading, though.

dont get me wrong I really do enjoy all the free A/C equipment (most of it I end up giving away to people who do want it.. I had enopugh stuff to outfit a church bus this spring.. all we had to buy was some wire and a few fittings and some hose..)..



I only have one more of my busses to outfit with A/C and that one will be a completely custom build to look identical to the factory-offered systems on that bus model
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Old 06-30-2021, 01:56 PM   #9
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2003, we converted a 1997 Ford CF8000 commercial truck to our concept of an ExpeditionVehicle.
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Summers up rough logging tracks to remote mountain lakes, winters on isolated Baja beaches.
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With nearly two decades full-time live-aboard, we prefer to follow the weather.
As you can imagine, we never much saw a need for an air-conditioning machine.
The complexity exceeds our 'simple living' philosophy.
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Old 06-30-2021, 05:04 PM   #10
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large marge in baja

I find the name fascinating. sounds like you have been runnin around in a home built motor home for quite a while. Thanks for adding your input

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Old 07-26-2021, 04:42 PM   #11
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One of the first things I did was rip out the THREE factory air systems because they're worthless unless you're driving. Hundreds of pounds removed, lots of space opened up. Two 9000 BTU mini splits will be just fine when parked as well as on the road.
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Old 07-26-2021, 06:26 PM   #12
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two 9000 BTU minisplits will choke on the road unless you plan to stay above 5000 feet all the time through summer.. everyone (except ohio) is having a really hot summer.. ive gotten requests for quite a few A/C units where people are not staying cool with camper units or they ripped out their old ones and are roasting on a minisplit..



if you chase 80 degree weather you'll stay cool.. if you live in the reality of modern summer you will be stopping to buy sweat rags..



or you can go to ohio where the summer is quite depressing and worthless as everyobe else is having a wondertfully hot humid and baking summer while we havent had a single heat advisory or day above 95.. it just rains every few days.. today was nice tomorrow will be nice but its getting downright cold at night here (BS 58 tonight) so your minisplits would keep you cool here.



I need to find a state where global warming is real because its not here..
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Old 07-26-2021, 11:44 PM   #13
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Quote:
Originally Posted by cadillackid View Post
two 9000 BTU minisplits will choke on the road unless you plan to stay above 5000 feet all the time through summer.. everyone (except ohio) is having a really hot summer.. ive gotten requests for quite a few A/C units where people are not staying cool with camper units or they ripped out their old ones and are roasting on a minisplit..

if you chase 80 degree weather you'll stay cool.. if you live in the reality of modern summer you will be stopping to buy sweat rags..

or you can go to ohio where the summer is quite depressing and worthless as everyobe else is having a wondertfully hot humid and baking summer while we havent had a single heat advisory or day above 95.. it just rains every few days.. today was nice tomorrow will be nice but its getting downright cold at night here (BS 58 tonight) so your minisplits would keep you cool here.



I need to find a state where global warming is real because its not here..

9000 BTU is rated for 400-450 square feet with 8 foot ceilings. 400x8=3,200 cubic feet. The interior of our 40' skoolie is 7.5x39x6.2=1,813 cubic feet. With only 56% of the rated volume, a properly insulated skoolie should be fine with a single 9000 BTU heat exchanger provided air movement is incorporated in the floor plan. TWO of them should be just fine and provide our desired redundancy.



Now should the temp be 110F, well all heat exchangers are going to suffer in such conditions. Rather, they will still remove heat but the temperature drop may not produce the desired output temperature. That's just a physics issue dealing with the thermodynamic capabilities of systems based on a closed refrigerant based system. Which is exactly what the engine driven system is. A closed refrigerant based heat exchange system, just like a mini-split.



The most likely cause of poor performing mini splits in mobile applications would be contamination in the DIY installs by those without training and experience with HVAC or mobile AC systems)


No idea how 5000 feet would make much difference. Not very significant to a system that isn't ambient pressure sensitive and 5000 feet is only going to produce a 10 degree average reduction in temperature (standard lapse rate) plus a a few degrees for being further from urban/suburban heat sinks.
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Old 07-27-2021, 08:08 AM   #14
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Im sure that when the lab tested it, they included all the same variables. These tests were performed in a long, narrow steel building no thicker than 1-1/2", full of leaks and 30 plus windows. All durring 55 mph winds blowing through the structure and condenser coils.

Look above your amtram windows. 70ft of convection leaks. You may not know how wrong you are, yet. But you are preaching to thousands of veteran owners, who have tested your theory. Been there, done that, that dog dont hunt.

Surely you can relate to hearing a young cadet teaching the military way to retirees. Its entertaining.
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Old 07-27-2021, 08:23 AM   #15
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Im sure that when the lab tested it, they included all the same variables. All were performed in a long, narrow steel building no thicker than 1-1/2", full of leaks and 30 plus windows.

Look above your amtram windows. 70ft of convection leaks. You may not know how wrong you are, yet. But you are preaching to thousands of veteran owners, who have tested your theory. Been there, done that, that dog dont hunt.

Surely you can relate to hearing a young cadet teaching the military way to retirees. Its entertaining.
Couldn't say it better.

If you skin over 3/4 the windows, install r13 or better, and then use a non-thermal conductive interior. You'll want to consider floor insulation as well, because a lot of heat comes through that from the road surface too. And don't forget heat from the engine compartment either. Also, apply as much window tinting allowed to all of the remaining windows to cut down on uv/ir/heat from the sun.

If you do all of that, you have a chance.

A member here used to hang a big curtain behind the driver's seat, and coupled with a rooftop unit over the driver, they were able to be "comfortable" going down the road. Comfortable is in quotes, because we all have a different desire, but for the record, doing that won't get you 68*F with 50% RH in 90*F.
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Old 07-28-2021, 02:33 AM   #16
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Gentlemen, your assumptions of our build are apparently incorrect.


We're we are only keeping six windows behind the driver with four of them being emergency escape windows. They don't leak because they're (original) coach style windows but if they did, they wouldn't when we got done with them.



We're building a full blown Class A motorHOME based on the superior bones (compared to an RV) of a skoolie so we are in fact:
Insulating & sealing air tight w/ closed cell spray foam on walls and ceiling.
Insulating the floor with Fomular and sealing all joints
Installing a 100% coverage air gap above the roof
Adding additional insulation to the rear engine bay walls

Max reflective window film behind driver (security and environment)
Max legal tint in drivers area


The only operational difference between a mini split and a factory engine driven system is the source of compressor rotation. BTU output and distribution of treated air are the design considerations. Considering the change in mission (from cooling off 58 humans in a school bus with designed in air flow (open vents in the ceiling which we will be removing) to a closed, sealed, and well insulated structure with only two humans, 9000 BTU should have no problem.



As for the scenario of attaining 68F in 50%RH and 90F there are some factors unaccounted for. While I suspect that's easily doable as it's only a 20F drop. However I seriously doubt I'll have 50% interior RH and a 90F outside temp. I'm pretty sure RH is only going to affect the evaporator, not the condenser and the interior air will be continuously reprocessed removing additional moisture at each trip through the evaporator. In fact, we are considering a humidifier to prevent interior humidity from getting so low that it dries the nose throat and lips.

I suppose in a poorly insulated, leaks like a sieve, "build" a mini split might not work.....then again in such an environment what would without being a massive energy waste?
FYI, my first accredited AC training was in 1982.
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Old 07-28-2021, 08:17 AM   #17
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Classic Schrödinger's cat observer.
Most of us already know, that cat is dead. Once you look in the box, you too, shall know the truth.
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Old 07-28-2021, 08:36 AM   #18
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it sounds like a dark cave being built.. not saure id want to drive / live in that.. (6 windows total).. at any rate you have a valid shot.. I still stand by the notion of adding or modifying a dashboard A/C system.. I drove many a trip in a Professionally built Prevost Motorhome.. it was built similarly to the build you are talking.. out of a rear engine Coach . that bus had 5 rooftop units on top.. and a few more windows..(double pane top notch RV type).. its owners believed in seeing the world not living in a cave..



I drove it no less than twice each year round trip from ohio to south florida and back.. one trip was always done in the height of summer..



on the hot days we ran at least 3 or 4 of the rooftop units.. sometimes all of them.. I ran my front engine-driven A/C on full blast along with the rooftop unit that was just behind my seat. the front engine driven A/C was rated at 24,000 BTU and each rooftop was 12,000 (or maybe 15 i cant remember).. with all 5 units and the front engine air we could literally make it 70 or below in there on a 100 degree day. thats in the living part of the bus.. so we often didnt run all the rooftops as I mentioned since the guys in the back didnt want to freeze (75 was more their deal).. up front i ran the system in Bi-Level mode when travelling southbound.. get to Ocala or so in the afternoon in may-august and you needed all you can get.. i was comfortably cool but I surely wasnt frozen.. that massive prevost windshield and large driver / door windows that were fitted custom were great for visibility but were warm in summer sun.



when I built my DEV bus system I remembered that Prevost.. so yeah i have 100,000 BTU of A/C in a 7 window bus.. cruising down through florida or texas in august is no big deal.. I get to see the scenery and enjoy the daylight through my big bright windows and still stay as cool as I want.
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Old 07-28-2021, 02:47 PM   #19
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When I hear the term "professionally" I often cringe. Professional just means they get paid to do it and to be frank, they're looking to profit, which means cheapest materials they can get away with. This applies across ALL industries and specialties. That half million dollar new home with the granite countertop and columns in front? Built to the exact same code as the 190k house in a different neighborhood. Never forget, the code is the MINIMUM acceptable safe standard...... which means its just barely okay.

That's the biggest reason we're building a Class A instead of buying a 40' fifth wheel which was the original plan until we discovered how horribly built (by professionals) they are.

Five AC on a bus tells me the insulation was minimal or non existent. Ours will have that air gap I mentioned. That keeps the suns radiant heat off the roof as well as snow in winter. This increases the total insulation system of the roof.
As I mentioned, we have Coach windows, not skinny school bus windows. The entire living room will have windows on both sides so combined with the driving area windows the front 15 feet or so will have windows on three sides. The bedroom will have a window on each side as well (and they aren't small). The Kitchen design probably doesn't allow for a window but if it will fit and be usable we'll put in a small one but it's right next to the living room and should have plenty of light and will be supplemented with LED lighting. The bathroom will have a small window for ventilation (6x12 or so) just because not doing so would be a mistake.

Plenty of light and only the kitchen will be "short" on windows. There would be fewer windows, and bars on them, if I had my way but it's a compromise with the other half.
That Provost sounds like it was built to plug in as soon as it arrived at the destination and at any midway points just fire up the generator. That's a pretty standard way to build things in the industry and for many people. We looked at todays big fifth wheels and frankly found them to be little more than weekend cabins and totally useless on the road. Kitchens, bedrooms, and even bathrooms inaccessible without running slides out (absolutely not acceptable for us). And those flip down stairs that can't be used in a tight slot at a rest area.... deal breaker.
Our rig is being built to be full time functional and livable while on the road (pull outs, rest areas, even WalMart) as well as in a static location for up to 30 days without resupply (that would be scrimping) with 14 days (the BLM maximum before moving) with ease. We will be relying on 2.5kW of panels, 10kWh of lithium, supplemented with a deployable windmill for those cloudy stays at the ocean and dreary winter days along with a small generator and an extra engine driven alternator (just in case).
The "mission" is to travel for three to five years including CONUS, Canada, and Alaska then convert to snowbirds.
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Old 08-02-2021, 08:21 AM   #20
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I got up close and personal with the test Bus (a bluebird vision) for electric A/C.. the design s for the bus to have road A/C and also parked A/C from the same system.. ProAir in elkhart and a company Vanner in columbus build it.. a friend of mine has the test bus and drives it all over the country testing it in various conditions and demo-ing it.



it uses 48 volt DC lithium ion batteries and electric compressors. the test bus has a 9kw generator engine driven.. read that as a 9000 watt alternator!! this thing is Yuge!! however the idea of solar to charge and supplement battery life is in the mix just not on the test bus. the evaporators and condensers are the standard bulkhead mount ACT units and ACT CS-2 condensers underneath the bus.. the test bus also has Dash A/C as well.. the bus was originally built with engine driven factory A/C and then retrofitted as a test to see how their system would do being retrofitted in..



ProAir makes a smaller system used in ambulances and smaller busses that is same principal. electric compressor run by an engine-driven generator and a battery pack.. everything is genberated as 48 VDC to minimize losses and use smaller wire sizes..
my buddy broguth the bus back to columbus for some updates.. his chedule was tight but is going to try and get me in on a class / demo once they get it done and he comes back..



its not for the Cheapsters out there but the technology is moving forward in an electric-friendly direction when it comes to A/C. the idea that a 9kw alternator can be spun by a normal CV8 serp belt and mounted on standard engine brackets is fascinating, which is the case for it,, mounted right up to the cummins 6.7 right above the 12 volt bus alternator.. apparently its marine / military spec. 200 amps at 48 VDC
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