Going to have to agree with this as I had never messed with an AC unit, refilled, vacuumed, any of that stuff, only experience I have was huffing freeon from them when I was a young teen. Luckily I lived through that and advise against it but recently bought an 07 pt cruiser and air didn't work but there was a full can of r134 in car when I bought it, I borrowed a hose with no gauges at all, seeing the sticker on hood told me it holds something like 16oz and this was a 12 oz can, did no more then skimmed over directions on can hooked up turned on full blast , closed passenger side vents which bottle recommended and it did make a huge difference getting the cool air to driver vents, every now and then rotated can from 12 to 3 o'clock as stated on bottle until empty. Had no ac now it's cold as ice. Definitely would not say there's much of a science to a simple recharge like that, no gauges needed, just don't use bigger can than your car holds. Basically follow directions and if all you need is a recharge it's simple, no other factors have changed the way it works afterwards, as in temperature or anything. If it's something more then just simple recharge I'm sure it could get complicated but from everything I've read if you can read and follow instructions, you should be good.