Went to a service call where the customer complained about their walk-in cooler not cooling. Upon arrival, hooked up gauges and noted very low pressures. Furthermore, I could hear a tiny hissing noise coming from somewhere behind the compressor along the back wall. I finally found this on the 1/4" liquid line (against the wall)...not quite sure how this would happen?
Anyways, cut out the section of copper and brazed connection...pressurized with nitro, checked for leaks, evacuated and charged...problem solved.