I arrived for a previous customer no cool call. I first spoke with the homeowner and four that the mini split in the shop will run but it starts to freeze up and it is not keeping the building cool. I inspected the system and found the system to be running at -4 psi and with a 84 deg superheat. I made it aware to the homeowner that the system has a refrigerant leak and we need to preform a leak search with a possibility of repairing the leak. We decided to agree to the leak search and see what we can do to get the system running. I first pressure tested the system with nitrogen to 500 psi and used a electronic leak detector and soap bubbles to locate the leak. I found the line set to be a plunger and piston precharged line set. I found the 1/4 king valve piston and plunger to be leaking. I removed all nitrogen from the system disassembled the fittings. I found the king valve fitting to be a 1/4 flair fitting that seats with a rubber O ring. I had a rebuild kit to rebuild a low loss ref