Works pretty good with soap bubbles. If you want to find small leaks, put a couple of ounces of refrigerant in with the N2 for a trace gas, I like R22 for example. An electronic sniffer can really vet out the leaks then. Using barrier hose on your gauge set will cut down false leads. Mechanical compressor seals will also "leak" a tad until things get moving and the seal is bathed in oil.