Depending on the system's location, freon can be a gas or a liquid. The leak will often start as "pinhole leaks" in the evaporator coil. The leak will first show up as tiny bubbles. In the evaporator coil, it is a superheated gas and will leak as such from the coil. However, if the leak is liquid, it is not in the evaporator coil, which is a fairly unusual location. Repairing leaks outside the evaporator coil is very expensive.