Why does my air conditioning only blow hot air? Just put 2 cans of freon in.

I don't remember, can't find my gauge. I'm not sure if it's a leak somewhere or if it's a bad expansion valve. How could I find out which one it is?

they sell freon with Flourescent Leak Detector Dye in it to help find where it's leaking.. you'll need the glasses and or black light to see it...