I know exactly how you feel. I spent all day working on a mini split for a server room. It got up to a whole 8º and it took a whole bottle of oxygen to heat the jug up enough to charge the system. I kinked the copper line 3 times, apparently copper don't bend in the cold. At least I left the vacuum pump inside 2 hours before I needed it, but I forgot to fill it up with oil that was in the tool box of my truck. I'm sure the system is over charged because of the added 75' of lineset, but I don't know what the subcooling is because it's too cold for my LCD readout to work on my thermometer. But at this point in the day I really didn't give a rats rear end if the subcooling is off and it was over charged. I had a 20º delt T and the Server room was sitting at 68º and my feet at -10º. I'll take a better look at the charge when warmer weather returns. I just hope I get a little more inside work tomorrow.
Get one of these. We use 'em all the time. Works like a charm.