Help please! A/C replacement issues

[CVaznis]

I am trying to replace the a/c unit on my '76 31' Sovereign. I ordered the Coleman Mach 3 Plus.

We removed the old unit and cleaned the surface of the roof before placing the new one on top. We lined the foam gasket up with the 14" hole however on the back side of the 14" opening where the aluminum roof is not braced, it has bowed with gap and the unit is not sitting flush with the roof. We watched a youtube video of an installation with the same problem and they made a brace for it but did not tell what they used or specifically what they did.

Anyone have some advice on this?

Christine

[CVaznis]

No one? I find it hard to believe that no one else has run into this issue while replacing the a/c unit. ??

[Iansk]

Originally Posted by CVaznis

No one? I find it hard to believe that no one else has run into this issue while replacing the a/c unit. ??

Folks are busy arguing about WD hitches and Tow Vehicles...

To be clear, you have no support at the rear of your 14x14 opening?

Post pics, that always helps.

I ran across this issue on my silver streak and used off the shelf aluminum square tubing from Home Depot and some stout rivets to shore that area up.

Each problem has it's own approach however, I am happy to help if I can.

Ian

[BayouBiker]

You can get some aluminum sheet and make yourself a brace out of that by forming it into a slightly curved I beam or square beam. rivet it together. You can also use lightweight wood like soft pine or similar. If you use wood be sure and varnish or weather seal it just in case you have a leak.

[CVaznis]

Thank you Brian and Ian for the replies! I appreciate it! I will update on what I end up doing to correct this!

[Belegedhel]

I'll second the use of a wood braces. It doesn't need to be anything exotic, just something to go between the interior ceiling skin and the exterior skin so that when you tighten down the mounting bolts, they have something to clamp against.

I think I used some hardwood, like oak, just to minimize the compression/shrinkage of the wood. I used a band saw to cut a very slight curve into it to match the curvature of the shell. As I recall, I might have boxed the entire hole, with two straight pieces on the sides, and two slightly curved pieces fore and aft. The wood I used was approximately 1.5" wide and 1.75" deep (to match the trailer wall thickness). Now that I think more on the topic, I might have even attached the four pieces together with pocket screws once they were in place.

good luck!

[A W Warn]

I've used wood, treated wood, and aluminum on different air conditioners I've replaced.
Don't make the mistake that I did, thinking treated wood is better, because it can be harmful to the trailer. The chemical used to preserve the wood can react and corrode a hole in the aluminum.
IMO, it is best to use wood or aluminum. Shape it to the curvature of the roof/ceiling. If the curve is so large that one gasket will not seal, use two.

ps:

Some trailers have ribs adjacent to the air conditioner opening. If your trailer does, you might consider that the front to rear blocking should be attached to those ribs to support the AC. I've created a channel out of two aluminum angles screwed together, cut longer than the space between the ribs. Then I create a support tab at each end of the channels by cutting/bending the ends inward. Drill holes in the tabs and attach to the ribs using a self tapping screw. I had to connect together a couple magnetic driver holders to reach in between the skins to drive the screw. Then rivet to the skin.

[CVaznis]

Great info Alan! Yeah, we decided wood would not be ideal. Any reason stainless steel would not work? I found a strap at Home depot that is 17gauge (I think, I don't have it with me right now) that is sturdy enough but flexible enough to curve to the roof. I will keep you posted and post pictures when we are done. We also plan to use them to stabilize the vent replacement.

Christine

[BayouBiker]

Don't use stainless. The metal dissimilarity will promote galvanic corrosion and the aluminum will loose especially since the edge of the cutout is exposed, plus the roof is exposed to the night sky there will often be condensation and humidity present. If you insist on non-aluminum metal, Insulate contact with strong shipping tape, insulate the fasteners also. Aluminum or lightweight (untreated as was pointed out) wood are your best options.

[TheGreatleys]

I framed out the hole with 1" square aluminum tube attached with sikaflex and pop rivets under the AC gasket. That seemed to help a lot with support (though it would have made more sense to use 1.5" tube to match the gap between the skins), but my rib placement may be different from yours.

If I had to add more rigidity in the back, I'd probably use 1.5" aluminum channel so I could extend the sides of the support further back to the nearest rib, and attach with buck rivets since some of the rivets would land outside the gasket.

Here's all my Mach 8 install blog posts. Reverse chronological order, so the ceiling framing is at the bottom of the page.

https://thegreatleys.com/journal/cat...Cub+AC+Install

[CVaznis]

thank you for the responses! I think the piece we are thinking of using is steel and not stainless steel so it is the same material as the frame.

Christine

[A W Warn]

Before installing the steel, you might read up on "galvanic corrosion between steel and aluminum".

The first Google search I did had this result: "different kinds of steel alloys and aluminum can cause severe corrosion, so it is advisable to provide insulation between the two metals"

[BayouBiker]

Originally Posted by CVaznis

thank you for the responses! I think the piece we are thinking of using is steel and not stainless steel so it is the same material as the frame.

Christine

The frame is aluminum I believe, I would be totally surprised if any of it were steel. Carbon steel is much worse than stainless when it comes to galvanic corrosion.

[CVaznis]

This is what I have found on what an airstream frame is made of:

And that's where it all begins. Each*Airstream*features achassis*built unlike any other, a ladder-frame*steel, free-standing, self-supporting*chassis. Welded steel outriggers are utilized for additional support and strength, and the*chassis*has a corrosion-resistant coating.

The shell of an*airstream*is*made*from a high quality “aircraft grade” aluminum alloy riveted over a steel frame. This is insulated and then an inner shell of aluminum is riveted on from the inside. Not only is the material more expensive than what other brands use, but it also takes a lot more labor to assemble.

[brokeboater]

I've redone a few 25' Safaris, including stripping the accumulated 14 layers of caulk around the roof vents. They are built the same way, aluminum frame on one end and the sides, none on the other end. This invariably causes a sag at the unsupported end and a great place for water to sit hoping to find a place to leak. I typically build a brace out of wood. To get the curve I just cut a series of graduated cuts with my table saw. It only takes a few. I screw the two corners of the vent frame into the wood support first which forces the ridge of the support up to support the middle of the roof where the sag is. As it supports almost no load it works just fine to keep a peak in the roof in that area and keeps water from collecting. If you need to to add structural support for the back of the air conditioner I think I'd use aluminum tube of the same size as the frame. I'd make it wide enough to contact the for and aft running frame supports along side the air conditioner opening. I would then attach it with a strap on either end externally pop riveted through the roof and into both the existing roof framing and the added tube. You wouldn't really need to pop rivet it to the existing frame if you didn't want as the pop rivets through the straps/roof/support would hold the support in place. A little caulk strategically placed would solve any issues and it's all out of sight anyway. Good luck.

[CVaznis]

Originally Posted by brokeboater

I've redone a few 25' Safaris, including stripping the accumulated 14 layers of caulk around the roof vents. They are built the same way, aluminum frame on one end and the sides, none on the other end. This invariably causes a sag at the unsupported end and a great place for water to sit hoping to find a place to leak. I typically build a brace out of wood. To get the curve I just cut a series of graduated cuts with my table saw. It only takes a few. I screw the two corners of the vent frame into the wood support first which forces the ridge of the support up to support the middle of the roof where the sag is. As it supports almost no load it works just fine to keep a peak in the roof in that area and keeps water from collecting. If you need to to add structural support for the back of the air conditioner I think I'd use aluminum tube of the same size as the frame. I'd make it wide enough to contact the for and aft running frame supports along side the air conditioner opening. I would then attach it with a strap on either end externally pop riveted through the roof and into both the existing roof framing and the added tube. You wouldn't really need to pop rivet it to the existing frame if you didn't want as the pop rivets through the straps/roof/support would hold the support in place. A little caulk strategically placed would solve any issues and it's all out of sight anyway. Good luck.

Great info! Thank you so much!!