Hi tonga if I go through that are special cases where it is a micro micro micro leak, but the issue is when the refrigerator is working and has cold or heat in its pipes and / or in its stops or starts since many lose when they stop or when they start it depends place and I insist again ... when the change of temperature dilates or contracts the pipe .... With respect to the vacuum and prove that it does not move the needle you should know that it is not reliable 100x100 since the same oxide or corrosion of the puncture can make a plug if it is in negative pressure. It happened to me 2 times also with air conditioners that did not find the loss after reviewing everything and seeing nothing with the detergent, I took it home to disarm evaporator and immersed in the fuenton and nothing appeared UNTIL that changes the temperature to the water from cold to hot, there was the bubbling.