So, we recently purchased a Midea 12,000 BTU, U-Shaped Window air conditioning unit. (It's actually a mini-split type of AC, and it's fantastic)

During the install, I realized they assume you're going to mount the unit to a sill, that is a single window,  by screwing down the support bracket to either side of the window sill. 

This is fine, except in our case, we have double windows, and only want to install the AC in one unit.

So, while I was able to screw the bracket in, on one side, I wasn't able to do the other. So, I opted to design a couple simple blocks to act as support for the bracket, and drill through them into the base of the sill. 

This design is chamfered on one end, in case you have silicone sealant at the bottom of your sill (we do) and has multiple holes for placing screws through. 

Note, being that I'd read there were multiple brackets with some different spacing, I placed the holes irregularly spaced apart, to maximize the chances of having it work with other brackets (we have 3 friends that  have decided to buy these now, and as such, I wanted to make sure their brackets will work, too)

In our case, the 2 support holes that worked, were the far right hole (once closest to the edge), and the 3rd from the left. 
 

PRINT NOTES:

I've printed these with both a .6 and a .8 nozzle, but I imagine it'll work with smaller ones, too, if you'd like.

You'll want to measure the height from the bottom of your sill, to the top of the window crevice your windows closes into, and scale the z height, accordingly.  In our case, it was 33.6mm, but yours may be taller or shorter… adjust accordingly.

For strength, and full rigidity (as well as to handle drilling), I recommend 50% support, with 6 vertical parameters with a .8 nozzle, 8 vertical parameters with a .6 nozzle,  and 12-14 vertical parameters with a .4 nozzle. 

So, why so many vertical parameters? This support block may need to have its holes drilled out, to accommodate the screws you use, to mount it to the bottom of the sill, and support underneath the sill. Additionally, you do NOT want this sagging, or deforming in any way, since it's going to be partially holding that AC up.


I wanted to make sure this thing was solid as possible, and I could still widen the hole, since I wasn't sure where my horizontal stud started underneath my sill. As such, the holes I started with, as expected, had to be drilled out. 

If you need to post process with a drill, I recommend doing so by holding the part in a vice, and using something like titanium bits, to have less chance of the material sticking to the bits. (I've ruined a few normal bits this way)

IF you don't have a vice, you CAN, theoretically, place a piece of wood under the block, and apply downward pressure to hold it in place while drilling. 

Suggest printing in PETG,  that way it doesn't cost an arm and a leg to print, nor will it melt if you window gets overly warm/hot. 

Yes, the print suggestion is overkill.  I know this, but I'd rather have too much, than not enough. 

(Yes, I know the photo is absolute rubbish.. but i didn't really even think about publishing this mediocre design, until my friends asked for it, since they are in a similar situaion)

Also, one last thing.. the support bracket, when screwed into the wall on one side, and a support block on the other.. seems to have too much flex for me, so I printed 2 support blocks, one for either side, and also screwed it into the wall… however you want to do it, obviously, is up to you.