Closing in an exterior window

I see lots of tips and demos on how to create a window where there wasn't one before, but how about the opposite? I have a through-wall air-conditioner that has got to go. The location strikes me as an awkward place for a window, and besides, the opening is too small to accomodate any standard window I've found, which means $$$$$$. So that leaves closing it in. Doesn't seem to me that it ought to be complicated, but I feel unclear on certain details of the project, like how how much framing it needs (can I just sister in 2x4s around the opening to screw the drywall to one side and the sheathing on the other?) What insulation to use. How best to seal up the spot. How to patch up the vinyl siding on the outside. etc.

Any good place to look for pointers?

rabbit

 

Frame the opening with 2x stock to bring the wall to within 1/2 of the existing interior wall. Insulate with whatever that thickness is, and add drywall on the framing. The hard part may be getting the exterior siding to appear continuous. If the wall is brick or stucco, you need a mason to make it invisible, this is not a DIY job. Other types of siding are much easier.