When a thorough testing of the condensing unit doesn’t show a leak, move on to the evaporator section. Follow the same procedure as the one followed to test the condensing unit. You and the customer must be aware that leak testing of this nature is time consuming, and time is money. If the leak hasn’t been found after the condensing unit and the evaporator section have been tested, it is time to talk to the owner again. Obviously the leak is somewhere in the piping that joins the condensing section and the evaporator section. This type of repair is going to take a judgment call on your part. If the piping is mostly concealed in the floors and walls, it might be best to run new piping rather than breaking down walls and tearing up floors. It would be advisable at this point to make an isolation test.