If it is low on refrigerant, the compressor won't kick on (there is a pressure switch). You can get a can of refrigerant with a fill trigger and gauge for less that $15. It will allow you to check the pressure and add refrigerant if you need it. Older cars tend to have o-rings dry out and leak, but the re-fill kits have a conditioner that helps give the o-rings a little life. The problem is, I would think your car is too new to be experience something like this.
As far as more serious causes, I would look at any A/C stuff touched during the intercooler install. There is some "adjusting" of AC lines that occurred that I would look at. I actually had my hot-side intercooler pipe melt a hole in the A/C condenser. This happened because I didn't pay attention when removing and replacing the pipe one time, and installed it so that it was actually touching the condenser.