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Old 07-17-2020, 08:47 PM   #1
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Secure enough for external AC unit?

I have a mini split external unit that I will mount on the back of my bus at the top. I am going to run square steel tubing along the last six feet of outside top of roof and then it will protrude out behind bus and will hang external unit from threaded rod. The tubular steel will be bolted into two sets of roof ribs, and bolt and huge washer will go through into the bus right at two different sets of ribs. Are these ribs sturdy enough to use in this fashion?

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Old 07-18-2020, 05:21 AM   #2
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IF tied together properly, it might well be strong enough, but I wouldn't to it for three (or more if I think about it enough) reasons:

1. Despite tying together 3 or 4 roof ribs, the weight is going to hang on the last one, putting all the downward load on the back rib and pulling up on the rest. Worse, unless you use really tall beams (like 2x6 steel in vertical orientation) the beams (square tube, for example) will flex like a spring aggravating the problem, weakening and working everything loose. Remember, going over a pothole could put 1/2 ton of force into your roof structure even if the frame rails and compressor weigh less than 100lbs combined.

2. This cantilever design will amplify high amplitude shocks and vibration into (layman's terms- shake the crap out of) the minisplit hardware, which is designed to sit on the ground. Yes, they apparently survive pretty well en the road in many RVs and buses, but you're making an already difficult life a lot harder for the motor/compressor, bearings and tubing than it was ever designed for. Probably OK, but...

3. Even if its all done beefy and stiff enough, this configuration will be highly prone to creating roof leaks, especially over time and factoring in thermal cycling and corrosion.

It would be more prudent to put the compressor unit on a shelf or brackets that attach vertically to the back wall, or at whatever angle the back wall is, with vertical members that can carry the weight down to the floor or the frame. This is a pretty well-engineered setup, though it could probably be a little farther away from the back wall for better airflow:

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Old 07-18-2020, 08:26 AM   #3
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you definitely dont want to have your unit able to move or swing at all on the hanging threaded rod, the copper tubing is not designed to be continuously flexed.. it will cause the flares to leak or the pipes to crack
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Old 07-18-2020, 12:10 PM   #4
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AC external Mount

So, I understand and agree with both replies. I was a little IFFY on the proposal and that is why I posted it. In the mean time I have ten 375 watt solar panels on my bus currently making more electricity than I can use and a DIY Mr. Cool ready to install. I have no fear whatsoever of the AC install except where the hell to put the external unit.......

I have 3750 watts of solar on the roof, but with my two mppt charge controllers I can only harvest 2800 watts. With that being said it hits 2800 watts early and stays there all day. 1100 A/hr of lithionics lithium battery and a victron 5000 watt inverter. The charge controllers are victron 250/100 and my system is 12v (which is 14vlt near the top which is how I get 2800 watts. 100a x2 x14v.) Happy with the system except where the hell am I going to put my external unit?

I have did everything on the bus myself and have enjoyed every bit of it. The last 'stumper' that took a while to figure out was the solar racking. I took 2 months sorting that out in my head. I have no interest in looking at my uninstalled AC while I wrack my brain trying to figure out where to install external unit. I have a rear pusher and engine compartment door makes lower on the rear a no go.

I want it to have plenty of ventilation so I really want it mounted 'outside' somewhere. I have understorage but do not want to clog it up with my AC unit. Roof is not an option because I do not want to add height to my bus.

A bit stumped. Thanks for the input and it felt like it might be a 'no-go' with my idea and that is why I put the question to you fine people!!

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Old 07-18-2020, 12:13 PM   #5
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Thanks

TomA

Quote from TOMA "It would be more prudent to put the compressor unit on a shelf or brackets that attach vertically to the back wall, or at whatever angle the back wall is, with vertical members that can carry the weight down to the floor or the frame. This is a pretty well-engineered setup, though it could probably be a little farther away from the back wall for better airflow:"

Watched the video and it is an ingenious mount. I cannot do that because my engine compartment door opens and would hit the vertical mounts!
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Old 07-18-2020, 12:52 PM   #6
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What about on the driver's side of the engine bay? That's where Thomas put the compressor for the factory A/C. All you'd really need to do is reroute the intake snorkel and air filter. There's plenty of space and the panel is already ventilated. I would pull air in and blow over the engine, which is the way it vents already. Secure and out of the weather.



Downside is it might not work very well while driving, and of course if your bus already has an A/C compressor there, there's not enough room.



If that won't work the bus is plenty strong above the engine. If it were me, and I couldn't put it in the engine bay, I'd probably pull the rear window and surrounding skin off the rear panel, add some more vertical members between the cap and the shelf above the engine, brace them forward with some diagonals down to the shelf, weld brackets for the unit to the verticals 6" above the engine bay door and braced diagonally upwards, and reskin the rear panel over that with no window. Its involved, but not as bad as it sounds, depending on your skills and how persnickety you are about such things.


Just my $.02...
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Old 07-18-2020, 04:17 PM   #7
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a minisplit isnt really going to work very well while driving anyway.. you need way more A/C than that little thing can put out to cool the bus on the road. in the engine bay you have to contend with dirt and grime.. you'd defimitely want it sideways with the coils facing the outside of the bus, otherwise if you can reach all the connections for pipes and wires then its likely a nice solid place for it.
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Old 07-21-2020, 11:27 AM   #8
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Thank you for your replies

I still am stumped. I don't weld. I really want to do it if I can without welding.

Agreed about it not doing much driving down the road. I am not too concerned. I do not have any factory air. I am content driving with some windows open, no worry about the heat. I just want to be able to AC while parked, boondocking or otherwise. I also have the bus habitable 24/7/365. (I am not always in it, but I want it continuously climate controlled. (wont keep it human temp comfy when not in it, but will probably not let the bus get over 85 or under 55 (55 was the lowest in the bus that it was all winter, thank you chinese diesel heaters!)

This is bugging me a lot not having a plan for external unit. Like I said, solar roof racking took a while for me to sort out, but I like the final result.

I will shoot a short video of the mounting options. I guess I am mostly set on installing above window in the back, but appreciate that I have not come up with a plan besides cantilevered from the roof which for reasons already discussed probably is a bad plan.

Sitting here with lots of time to work on the bus and no plan.

(Maybe I should just finish the flooring. (work on the next test question as it were and come back to AC later.))

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Old 07-21-2020, 11:44 AM   #9
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Quote:
Originally Posted by Mark Miner View Post
I still am stumped. I don't weld. I really want to do it if I can without welding.
I used SuperStrut to mount mine, no welding required:



https://www.skoolie.net/forums/f11/k...tml#post356910

https://www.skoolie.net/forums/f11/k...tml#post378461
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Old 07-21-2020, 11:55 AM   #10
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At one time I was going to put a window unit recessed into the rearmost driver's side window. You could do something like that, build a compartment recessed into that back side window area to put the compressor in.
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Old 07-21-2020, 01:23 PM   #11
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I didn’t see what bus you have...but on my Thomas I mounted one fwd and one aft directly to the skirt. Cut hole same diameter as the fan exhaust and sheet metal screwed right to skirt. I did remove a rib to allow it to lay flat against the skirt but ended up not being necessary since I didn’t want to remove a rib in the rear and it mounted right up anyway.
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Old 07-21-2020, 08:54 PM   #12
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[QUOTE=kazetsukai;397308]I used SuperStrut to mount mine, no welding required:

Thanks for the good idea. I am going to look and see if there might be room on each side of the motor hatch to catch the strut!!

You have a very nice bus build.

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Old 07-22-2020, 09:00 PM   #13
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Kazetsukai idea works for me.

[QUOTE=kazetsukai;397308]I used SuperStrut to mount mine, no welding required:



Ok, so I am going to do just that. I will mount the shelf just above the rain gutter above the window and secure it to the bus. Then will have struts that connect down to the points just on either side of the motor hatch. I can then hang my bike from underneath it as well. The two sides by the motor hatch will be diagonal to hold up the rear of the shelf.

Just watched some superstrut videos on youtube. Looks fun to do as well!

Photo of plan. And photo of 10 panel install. One is series of 5 385w and other is series of 5 360 w.

Mark Miner
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File Type: jpg MIN04663.jpg (274.3 KB, 25 views)
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Old 07-23-2020, 07:56 AM   #14
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Make sure to keep the trailing /QUOTE tag. You can erase bits in the middle.



Quote:
Originally Posted by Mark Miner View Post
Ok, so I am going to do just that. I will mount the shelf just above the rain gutter above the window and secure it to the bus. Then will have struts that connect down to the points just on either side of the motor hatch. I can then hang my bike from underneath it as well. The two sides by the motor hatch will be diagonal to hold up the rear of the shelf.
Sounds/looks solid.





Quote:
Originally Posted by Mark Miner View Post
Just watched some superstrut videos on youtube. Looks fun to do as well!
Like an adult Erector Set!


Quote:
Originally Posted by Mark Miner View Post
And photo of 10 panel install. One is series of 5 385w and other is series of 5 360 w.
You beat me with that layout, I was overhanging in the rear 2' and could only fit 10 305W panels.


Good luck!
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Old 07-25-2020, 07:04 PM   #15
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It could go under the bus also with a vented door ,at least that's what I'm thinking of
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Old 07-26-2020, 02:41 AM   #16
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Quote:
Originally Posted by Mark Miner View Post
So, I understand and agree with both replies. I was a little IFFY on the proposal and that is why I posted it. In the mean time I have ten 375 watt solar panels on my bus currently making more electricity than I can use and a DIY Mr. Cool ready to install. I have no fear whatsoever of the AC install except where the hell to put the external unit.......

I have 3750 watts of solar on the roof, but with my two mppt charge controllers I can only harvest 2800 watts. With that being said it hits 2800 watts early and stays there all day. 1100 A/hr of lithionics lithium battery and a victron 5000 watt inverter. The charge controllers are victron 250/100 and my system is 12v (which is 14vlt near the top which is how I get 2800 watts. 100a x2 x14v.) Happy with the system except where the hell am I going to put my external unit?

I have did everything on the bus myself and have enjoyed every bit of it. The last 'stumper' that took a while to figure out was the solar racking. I took 2 months sorting that out in my head. I have no interest in looking at my uninstalled AC while I wrack my brain trying to figure out where to install external unit. I have a rear pusher and engine compartment door makes lower on the rear a no go.

I want it to have plenty of ventilation so I really want it mounted 'outside' somewhere. I have understorage but do not want to clog it up with my AC unit. Roof is not an option because I do not want to add height to my bus.

A bit stumped. Thanks for the input and it felt like it might be a 'no-go' with my idea and that is why I put the question to you fine people!!

Mark Miner
Have you considered enclosing the space above your engine and exposing it to the outside. This how I am handling it with my International RE. My rear unit sits on the shelf behind the rear seat. That is enclosed with plywood and 2inch polyfoam insulation board. I left the rear window intact because it swings open. I open it when I am running the A/C. Ok truth, I just leave it opened. It protects the outside unit from the hazards of hanging on the outside of the bus and is easy to access if I need to do any maintenance.
It even left some space above it for storage.
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Old 07-27-2020, 06:18 PM   #17
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Superstrut it is!

Still have to make a platform with extruded steel and one more cross bar, but DAMN. Thanks Skoolie people and Kazetsukai!
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Old 07-27-2020, 08:46 PM   #18
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I did the same test on mine


Nice work!
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Old 07-28-2020, 06:53 AM   #19
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just remember thats only part of the forces.. that looks plenty strong, however when you are bouncing you are creating shock or impact force as well.. the weight is multiplied when you hit a massive road divet...
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Old 07-28-2020, 09:46 AM   #20
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just remember thats only part of the forces.. that looks plenty strong, however when you are bouncing you are creating shock or impact force as well.. the weight is multiplied when you hit a massive road divet...
I tried to upload a pic of my suggestion last week, but it failed. Internet connection is very poor on this site lately.

It is very much like your solution, but also included the original brackets from the roof like you had originally suggested. I think that will definitely help with the vibration/bounce effect that I believe you WILL still have with this new design in your photo (but better than the original).

And as Christopher said earlier, the vibrations though the hoses can harm/crack the copper tubes and connections in the condenser. I think you should use these clamp-able inline splice connectors:

https://coldhose.com/specialty-fitti...e-splicer.html

You can find them on eBay also, and I'm sure other places.

Use one on each barrier hose after it comes out of the bus shell, as close to the end of the hose as you can (a foot or two). Clamp the fitting to the frame you built, or better, to the condenser itself.


Great job on what you've done so far! And without welding! Excellent!



But I suggest that you get over your fear of welding and learn how. It opens up so many new worlds. A cheap stick-welder is all you need to get started.
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