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Never had a leak like this. When I install a new system, I pressurize the lineset with 200# of pressure with nitrogen before evacuating. I did that with this job and it seemed fine. To make a long story short, I had to go back several times over the last couple of months to re-fill because there was a leak. This is a townhouse so lineset couldnt be replaced because it was ran in the walls. Today I cut the liquid and suction lines at the evaporator coil and brazed the ends shut, then pressurized each line seperately with 300 psi. Obviously I pumped down what refrigerant was in the system first. Sure enough the suction line dropped about 30 psi in an hr. Liquid line held. Why didn't this show up in the original test I did? The vacuum even held under 1000 microns for over a minute.