it usually comes out, and you cant really tell, other than the can getting lighter. 3 cans seems like alot. I used only one. U are suppose to let your A/C run for 10-15 minutes. And basically i pumped some for like 30 seconds, then went to feel the air, repeated this til it was nice and cold. If u put too much, it can be bad. Oh and i bought the one with the hose already attached.