Cutting the hole

[Airbag]

I am awaiting my roof air that I have decided to install in the back of the bus which will require cutting the roof. Now me and my simplistic brain have been thinking, no problem just cut a hole and bolt it up but it's not going to be that simple is it? I know enough to stay away from the center spline or longeron. I am thinking the roof skin to be about .063 thick? What am I in store for? Will I be fabricating a frame for the cutout?

[Jriddle]

On my middle and back AC units I did cut the center rib to keep the AC unit in the center of the bus. I welded 14"X14" frame then drilled through the skin on the top and added rivits into my new frame. I can take some pics if you would like.

John

[Airbag]

That would be great John I haven't done this before and any ideas are welcome, thanks

[John316]

When we put our five roof airs on (I know, it is an overkill, so you all don't need to tell me) we cut the center rib. We welded it up similar to John's but we carried our lengthwise supports all the way to the crossway ribs. That way the stress is carried to two points, as opposed to the one point like the center rib has, and of course we finished the box too, so the AC itself was supported. I think that it is now stronger that when there was just one center support...

BTW, it wasn't my idea (rarely are things my ideas), it was our welder. That guy is incredible, and has been around since they invented welding .

God bless,

John

[Tenor]

Yup,
welded 3 14 x 14 boxes and welded them to the longerons for 3 roof airs.  Easy if you can weld.  Go for it!

Glenn

[jjrbus]

Weld in the two new pieces and then cut the center spline/longeron.   HTH  JIm

[busshawg]

I also cut my centre beam and welded in 2 pieces to go full length between the ribs 14 " apart, and then welded in by cross pieces to make my 14' x 14' mount.

Having said this I am planning on putting another in and am thinking I will leave my centre beam intacted.
I will TRY simply cutting my hole, place supports inbetween the roof skin and interior cieling ( probably pieces of oak) and modify the duct (usually foam piece) to accomidate the centre beam. My thoughts are that nobody will see the beam and the bus structure will remain intacted. Not sure how this will work but I'm going to give it a shot.

Grant

[Airbag]

Thanks all I see how it is done, My delima is the bus is a completed conversion with carpet and insulation on the ceiling. I think welding is not an option for me without some major disassembly. I will keep you all posted on my progress what ever route I take. Thanks again for pictures and advise.

[John316]

I agree, you do have a little fun issue . Let us know what you decide. Nothing is easy .

I hope things go well.

God bless,

John

[Len Silva]

Rick,

If you are working in a finished bus, then the only practical solution I see is to go off center. Cut the 14 x 14 hole through, then use wood cut to the ceiling contour to fill the gap and support the A/C.
I would use PT but cover it in plastic where it contacts the metal roof. there may be some corrosion issues between the PT and the metal roof. You also have to figure out how you are going to get the wiring there without tearing anything up.

[Airbag]

Hi Len
I was sitting in the back of the bus this morning and have decided to offset it anyway. It will line up with the hallway just slightly to port. The sliding bedroom door track will interupt the flow of air to the front but I think if I angle the vents down a little they will get the air past it. Now all I have to worry about is the wires and I think I can snake them under the carpet on the ceiling. I just have about a foot or two till they are in the closet where the breaker box is located. I wanted to get the split system working but I can't get anyone willing to work on it here in Tucson this time of year. The AC guys can pick and choose their work right now so I will wait till they are hungry in the winter. The roof unit should do the trick for the rear of the bus for now.

If anyone is thinking about ordering a Dometic AC right now you will have to wait longer than normal for it because their plant in Mexico burned down along with some semi's loaded with new units. Just my luck  They now are forced to build them in the USA I don't wish that bad luck on them but built in USA is A-OK with me.

I meant to ask what radius can you get away with in the corners of the cutout? The PDF manual I down loaded does not tell you.

[belfert]

On my bus I have trusses under the windows like the newer buses so the roof doesn't seem to be nearly as critical.  I just cut through the center beam and then welded in a 14" box made from tube steel.  The center piece of steel is thin I'm pretty sure it isn't keeping the bus together.

[gus]

Rick,

This should be a snap for you. Just cut the hole away from structural members and make a nice doubler of 0.060" Al or heavier.

We GMC nuts have an advantage, GMs have two smaller longerons instead of the one big one on MCIs so we can cut in the middle.

[Ednj]

I can't tell you how many times I've posted these picture's. 

[Ednj]