Last friday i started pressure testing a carrier 19xl centrif after rebuilding the compressor,we pressured up to 1104.1 kpa then myself and my collegue went over the system with a fine tooth comb checking for leaks using leak spray,no leaks were found however when we returned to site yesterday the pressure had dropped by 21kpa(around 3psig) so off we went looking for a leak then bingo we found a leak on the condensor releif valve reducing bush which definateley wasn't there on friday, it took both of us with a little help from my 2 foot stillsons and a scaffold tube to remove the 4" bush so basically what i'm asking is there any logic/cause behind this leak or has this happend to anyone before. like i previously said the leak wasn't there on friday