I gather what you are saying is the opening over the top of the slide is sagging due to the weight of the A/C unit that sits over the slide opening, therefore preventing the slide from extending completely.
Given the thickness of most of the ceilings in the RVs I would think the 'beam' isn't very heavy at all. The problem seems to be the incorrect location of the A/C causing this. I know, it obvious......
Without seeing the ceiing I would guess a relocation of the A/C, if possible, would be prudent. The sag then may be removed by replacing the sagging support material inside the ceiling, however that probably would require a removal of the slide entirely to gain access to the sagging material. Then there would be the problem of attaching the new support to the roof trusses. Or as a last ditch effort some sort of support material on top of the roof that is attached to the ceiling beam. This material would need to extend beyond the roof trusses for end support. Other than removing the slide, as I picture it, whatever goes on top of the rig will be a fix but it won't be pretty. However, this may be the only easy fix. The outside, on the roof would be my way to go if possible.
The rig is out of warranty so you will be on your own and probably looking at a wad of dollars to get it right.
This is a problem for sure and I'm sure the manufacturer won't be of any assistance to you.
2013 Voltage 3800, 2012 Chevy 3500 HD
2010 Yamaha V Star 950
2009 Yamaha Raider
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