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Old 04-08-2006, 11:01 AM   #1
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AC units

I just bought a 15,000 BTU roof mounted air conditioner for my skoolie and it weighs a ton! Any ideas on the technique or the need to reinforce the roof to mount it? You would have to cut the central roof support to install it.

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Old 04-08-2006, 03:36 PM   #2
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Roof AC unit

The standard roof AC unit weighs about 275 pounds. The mounting hole required is 14 X 14. Care should be exercised in unit placement. Many buses have a center roof support from front to rear. This support may be cut with no difficulty. After cutting support, there are additional supports fabricated to support the AC unit. The AC unit must be completely supported with steel material that was used by bus maker. Copying the methods used by the bus maker is always a good plan. The framework around the AC unit can be weldee in place or the pieces can be bolted. Using some 1/8 X 2 X 2 angle steel can be nicely drilled and bolted at the corners and will provide a very solid frame for the unit. Usually the RV type roof units are held in position with 4 long bolts which compress a thick roof seal between the AC unit and the roof. The wiring for the unit should be at least #12 wire as the unit has a high start up amp draw. I have often used good quality power cord for wiring. There are just 3 wire connections needed but the wires should be crimped, soldered, or connected with quality wire nuts and taped. Making wiring connections that are very substantial is very reassuring, as poor weak connections can ruin your day. Frank Electrical contractor over 30 years....
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Old 04-08-2006, 07:38 PM   #3
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Thanks Frank!

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Old 04-08-2006, 08:31 PM   #4
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My 1992 bluebird didn't have a center roof support, just had the bows from one side to the other. All I did for support between the two metal panals was used pieces of 2x4's all around and screwed them in place. The rv builders do pretty much the same thing between their exterior and interior roof. And then they drill a hole through the wood support for the wiring to go through. I miss measured mine slightly and it is slightly to the right side but it will still work since it isn't too fussy like a refrigerator running off propane is.

To cut my hole I started on top and used a electric grinder. Once my first hole was cut I drilled holes at the corners to tell me where to cut from underneath. I personaly like using the thinest grinding wheels since they cut the metal the fastest.
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Old 04-08-2006, 09:40 PM   #5
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Making a AC unit hole in da roof

I have cut lots of AC holes. My method is to start by deciding the total number of units to be installed. The front unit is usually the most critical as this unit is often used while traveling down the concrete ribbon. After deciding the exact postion from inside the bus, by measuring from some easy reference, I get on a ladder. Usually the center of the roof is easy to locate because of the roofing material. I have a sheetmetal pattern that I use to locate the corners. The pattern has some marks showing the cutout hole center. The pattern is laid on roof centerline and the corners are marked. I drill some 5/16 holes at 4 corners and get my Bosch jig saw. This is a great tool. I use a 18-24 tooth blade at medium speed. The blade is allowed to cut slowly and carefully. Cutting thru aluminium, steel, wood or plastic, the cut is beautiful. The roof hole falls into bus in a single piece. The support around the hole is very easy to complete. I have not used any wood as there are too many variables. Over time, the wood may self destruct, crack or fail. An after the bus is finished repair is a tough job. If the AC unit comes loose, it could fall off bus to the road. Frank
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Old 04-09-2006, 06:41 AM   #6
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Would it be better to cut through one of the roof ribs and bolt the metal frame to it and to the center support (if it's there) for added strength, or cut where there are no ribs? And any suggestions on how to get a 275 pound AC unit on your roof?

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Old 04-09-2006, 11:47 AM   #7
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Roof rib cuts

Usually the opening for a roof AC unit will NOT require cutting any ribs. The required opening is just 14 X 14 inches. Move the location to prevent any structual rib cutting.
Getting the AC unit on the roof is a real pain. The method I use is to lean an entension ladder against the side of the bus with some cardboard taped to the top of the ladder. The ladder angle is a very slow shallow pitch. I tape the ladder so that the ladder cannot change size. I have used some refrigeration cardboard doubled with a hole made some 6-8 inches from the front of the cardboard, in the center. A rope is thrown over the roof of the bus from the bottom of the ladder to the opposite side. The rope is tied to the cardboard slide and to the AC unit. Two people at least are required. One person pushes the AC up the ladder while a helper pulls the other end of the rope. With a co-ordinated effort the task is simple and easy. The AC unit will not fall off the roof. Place the roof seal in position and install the bolts. Care should be used in tightening the long hold down bolts. I usually do not crush the seal very tightly. In the future the seal can be tightened again and again in small actions. If possible, operate the AC unit immediately to observe that the unit works OK. After a short 15 minute trial, make all the connections permanent.
I have had 2 units out of many not work or no cool upon initial installation.
Some roof units need a drain pan to divert condensation water away from unit base. Frank
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Old 04-09-2006, 10:44 PM   #8
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Re: AC units

Quote:
Originally Posted by shaggy
You would have to cut the central roof support to install it.

shaggy

IF you stand on the roof and look at the rivets, you can see where the beams go across the roof. I've torn three buses apart, all were different bodies, and none of them had a center support. All had 2 supports that went the length of the bus but they were halfway between the center and the wall. They also had supports running perpendicular from the edge of each window.
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Old 04-09-2006, 11:44 PM   #9
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pjespers wrote:

Quote:
I dont have the headroom to use a roof mounted AC unit. Does anyone out there have any tips or advice for using a window AC unit? Perhaps one mounted in place of one of the rear windows?
Check out Steve's installation in the gallery. I'm thinking of doing the same thing that he did.

http://www.skoolie.net/gallery2/air_conditioner
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Old 04-10-2006, 04:41 AM   #10
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Quote:
Originally Posted by pjespers
I dont have the headroom to use a roof mounted AC unit. Does anyone out there have any tips or advice for using a window AC unit? Perhaps one mounted in place of one of the rear windows?
Also, you might take a look at Ken Thrush's "The Situation Room" in the gallery here: http://www.skoolie.net/gallery2/Skoolies
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Old 04-10-2006, 06:32 AM   #11
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I looked and don't have any central roof support. I think I am going to go to a metal shop and get some 2x2 angle iron welded into a square with the inside dimensions 14x14. At the peak of the bus there is still a slight curve. If I bolt the steel square at the peak and then tighten it down at the corners it will tend to buckle or distort the roof. Should I put spacers at the corners for the bolts so that this doesn't happen?

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Old 04-11-2006, 11:01 AM   #12
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curved bus roof

For the curved aspect of mounting your ac unit, there are a number of companies that make ac shrouds and foam gaskets. With those kits you get additional shims that run down both sides. I just looked up the part and a company called ventmate makes them. I happen to be at work and was able to look into it .

-Richard

Edit - I talked with a couple of journeyman rv mechanics and they will try to use the foam gaskets, they are good for up to an inch gap. Most said they have never seen a unit in which that was nessisary. If the gap is larger they would build a custom box made of 2 by 4 that could be shaped. Then seal it up well with paint and such. Another material they use is the cutting board material. It works well for shims on the exterior like awnings and such. Cuts well witha table saw and is sandable.
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Old 04-13-2006, 05:43 PM   #13
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Quote:
Originally Posted by pjespers
I dont have the headroom to use a roof mounted AC unit. Does anyone out there have any tips or advice for using a window AC unit? Perhaps one mounted in place of one of the rear windows?
check out how I did mine, it works quite well.
http://www.skoolie.net/gallery2/Big-Blue/100_6132
http://www.skoolie.net/gallery2/Big-Blue/100_5906[/url]
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Old 04-14-2006, 02:48 AM   #14
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Hey Brad,

I knew there was someone else with a regular window A/C but, I couldn't remember who it was. Sorry
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Old 04-14-2006, 08:26 AM   #15
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What the heck kind of roof air do you have that weighs 275 pounds?

Every unit I've looked at for possible installation has been right around 100 pounds (give or take 20 depending on the unit). They've been making them the same way for so many years (my classic 1977 Class C Beaver has one) it doesn't seem the older models would be that much different in weight.
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Old 04-14-2006, 02:20 PM   #16
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Quote:
Originally Posted by Les Lampman
What the heck kind of roof air do you have that weighs 275 pounds?

Every unit I've looked at for possible installation has been right around 100 pounds (give or take 20 depending on the unit). They've making them the same way for so many years (my classic 1977 Class C Beaver has one) it doesn't seem the older models would be that much different in weight.
I'd have to agree with that. My coleman 13500 can't weigh in much more than 100 pounds. I don't think it weighs anymore than a window unit for a house.
And now that I think of it the stick and staple rvs only use wood for spacing with no ill effects. And how many rvs use wood on the inside for building with no worry about how well it holds up in the long run? I really don't think metal supports are needed for a roof ac install.
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