No leak for more than a year. It was low because probably for 18 years it wasn't properly charged. There is always is some long term leakage (compressor shaft seal for example). I just can't emphasise enough that it needs 2.4 lbs and that's a lot. I can say more but do you know what "latent heat of vaporisation" is?Did you ever find out why it was low ? Was there a leak ?