I don't know about your particular model, but on the AC stuff, the low pressure side is usually the bigger valve, the high pressure is the smaller valve and as mentioned earlier, you want to put it in on the low presssure side.
You should have the AC on when adding the can. I'd have the can right side up first, then once you have it connected, you can flip over the can and it'll suck it right in although I've known people to just leave the can upright and let it take it's time going in. It might be less dangerous that way as I suppose things could happen if the system was already full and you overcharged it.
There's typically some sight glass somewhere that will show bubbles if it's not full. If it's completely hot air, everything could have leaked out over the winter and it would probably take 2-3 cans to completely fill it up although when this used to happen to me, I'd just put one or two cans in until it got hot again. Of course once the leak got pretty bad and it didn't last more than a few weeks, I finally got it fixed and it was fine after that.