To leak test the entire system, leave all valves open with the keg couplers in on position. Be certain that no one is dispensing while testing. Turn the gas cylinder wheel off and observe the high pressure gauge (indicates pressure in cylinder). If the needle begins to drop, you have a leak somewhere in the system.
To isolate, turn all the valves off and raise the handles on the keg couplers turning beer off but leave them in the keg well. Turn the wheel back on pressurizing system and then again turn off noting the needle on the high side gauge. If it drops, your leak is right at the regulator since the shut off below it is in the off position.
If it does not drop, your leak is downstream. Open the regulator shut off and repeat turning wheel on and off. Continue this process until you isolate where the leak may be. Using leak detector soap or other detection device, find and repair. Be aware that the leak could reside at the coupler or even the keg itself.
Scott Zuhse, Instructor
Micro Matic Dispense Institute