Bracing for new air conditioner

[L.D.Clara]

I've been reading a lot of threads about replacing the old Armstrong air conditioners and the need for bracing. The old unit on my '68 sovereign was not working and worked even less after it fell on my head and gave me a freon bath in the process of removing the inner skins to reinsulate. I plan on fitting the new unit in the same place as the old one, with the opening for the new one encompassing the two holes left by the old Armstrong unit
I understand that I have to create a 14" square opening and brace between the two skins to take the compression of the unit bolting down. I also gather that the sides of the hole should be formed by stringers ruining from one bow to the next, then crossmembers between them. My questions are that since the bows are about four feet apart, how does one get the stringer down there past all the insulation between the skins; and secondly, how do you actually attach the stringer to the bow?
I had thought that if you got the stringer right up to the bow and then riveted to the shin it would provide some support, but this would place a lot of shear load on a small part of the skin which might lead to problems.

I'd much appreciate any insight anyone can give on this, because I'm thinking it might turn into a major pain in the behind..

Thanks in advance,
Rob.

[ddstech]

It's not as complicated as we tent to think. From the factory it's a joke. I had a saggy a/c on my 58.

I took two pieces of thick c channel and ran them from rib to rib. Riveted them to the ribs using aluminum L brackets. And put two crossmembers between them to frame up the 14' hole. It's really strong. Once you rivet the two skins to the new framing it increased the strength even more.

This assumes you have removed the inside skin.

[L.D.Clara]

Originally Posted by ddstech

It's not as complicated as we tent to think. From the factory it's a joke. I had a saggy a/c on my 58.

I took two pieces of thick c channel and ran them from rib to rib. Riveted them to the ribs using aluminum L brackets. And put two crossmembers between them to frame up the 14' hole. It's really strong. Once you rivet the two skins to the new framing it increased the strength even more.

This assumes you have removed the inside skin.

Thanks, what you suggest sounds pretty much like I'd envisaged. I also tend to agree there isn't much support there as standard, which makes me wonder why the old armstrong one didn't make the roof deform.

As you say, it's pretty simple with the lining removed, but herein lies the problem. I should've done this before putting the lining up again, but I didn't. Having wrestled with two 20' lengths of very floppy aluminium to try and line up rivet holes; persuaded insulation to stay stuck to the roof while I do so; and then popped innumerable rivets, I'm very reluctant to open that particular can of worms again.

My current plan (such as it is) is to create the 'L' you mention on the stringers first and then use a somehow vastly elongated nut driver to screw the 'L' into the frame with self drilling screws since it will be about two and a half feet down an inch and a half wide gap..

It will be interesting that's for sure...