how hard would it be to install air conditioning in a car that is salvaged...
 

...from the same year and model of car my car is a '91 civic with no air conditioning, and i know a guy who jsut crashed his '91 civic, and the air conditioning may be intact, how hard would it be to add into mine, and would it be possible to do at home?ALSO: there is a place for the A/C button, and i think there is a place for a fuse

I wouldn't really recommend trying unless you REALLY know what you're doing. Air conditioner systems are pressurized, and attempting to dismantle them can be dangerous.You would also have to deal with the new wiring (relays in the fuse block), and new heater controls.It's not a drop-in module, it's integrated into the rest of the car, and as such, will be rather difficult, but not necessarily impossible. At the very least, if you decide to continue, buy a factory service manual, or failing that, a Haynes manual.

It would be a major process and a pain in the ass, but it could be done.

it should be fine. but if your car didnt come with one you might need to mount it and add some things like a hole for your inside hoses.