i have an older central air system and this year is started to fail, so before i call out the big guns i want to see if i can fine the leak. i know it has one because i did put a gage on it and it was low on both sides. so i researched a bunch of leak detectors and none seem to have good reviews. i look at the low number first, anyway has anyone here used this one and of so what did you think of it? i can't seem to get any reviews for this unit. Snap-On Tools Pump Automatic Halogen Refrigerant Gas Leak Detector ACT5500. thanks.