You don't have to remove the dash but it can make it easier.
Wiring inside is easy. You just need to find the plug in the cabin which tells the ECU the aircon is on or off. It'll be taped up and sitting around behind the plastic most likely visible from the passenger footwell side.
Wiring in the engine bay is a bit harder as you have to pull apart the fuse box to do it and bundle the new loom into the car and fusebox. And then you have to figure out which wires are which and run them around the engine bay to to the aircon compressor, the extra fan infront of the aircon compressor, the AC reciever/dryer and of course the ground which goes onto the top alternator to engine block mount. All the plugs are different so its pretty hard to screw it up.
Goodluck.