Leaking line set: can leak's sound vibrations travel through copper?
Low pressure line will not hold pressure during nitrogen tests. It leaks down immediately. A distinct hissing noise can be heard in the HVAC equipment closet when nitrogen valve is opened. It sure sounds like the leak's gotta be there, but Tech cannot find a leak in the line up to the ceiling. He suspects leak might be just above ceiling in attic. After tech left, I crawled (army-man style as we have vaulted ceilings) into the attic and spotted what looked like a roofing nail going into the line, but it is a good 15 feet horizontally away from the furnace closet. Can the sound vibrations from a hiss travel through the copper and give the impression the leak is in the closet when it isn't? Roof was redone two years ago, and no A/C since. I can't get close to the nail to inspect due to ductwork and low clearance.
I'd prefer to have the line set repaired, otherwise we have to run a new one up the side of the house. Equipment is 19 years old, so a new system may be in the near future (if not imminent). I'm already into this for 2 hours of labor. Don't want to put good money toward bad. Existing system is R22 and will need 7lbs.
Thanks for any advice!