Nitrogen Leak Detector Test and Bubble Test. An AC leak test with nitrogen—the preferred test by MAXICON CAR AIRCON SPECIALISTS —adds a greater degree of clarity to leak detection, though for slightly more cost.With this nitrogen leak test procedure, the HVAC technician first removes any remaining freon and pumps compressed nitrogen into the refrigeration system. The leaks become audible because the nitrogen is held at a higher pressure than the refrigerant can operate under normal conditions. I