Turn on the compressed air and dab soapy water to all threads and also where airline enters fittings. Bubbles will form where there are leaks.
Leaks from threaded fittings
Leaks from airline
WARNING: HYDRAULIC AND PNEUMATIC POWER SYSTEMS CAN FAIL THROUGH MISUSE, AGE OR MALFUNCTION. THE SYSTEM DESIGNER IS WARNED TO CONSIDER THE FAILURE MODES OF ALL COMPONENTS USED IN THE DESIGN AND ENGINEERING OF ALL SYSTEMS AND TO PROVIDE ADEQUATE SAFEGUARDS TO PREVENT PERSONAL INJURY OR DAMAGE TO EQUIPMENT IN THE EVENT OF SUCH FAILURES