A "Liquid Charge" is any charging of the A/C system using Freon which enters the A/C system in a liquid state as opposed to a gaseous or Vapor state. This is most commonly done by facing any freon caninsters valve opening towards the hose connection so that gravity is moving the liquid through the hose. If the valve opening is facing upward only gas can go through the hose. Simple case of gravity and liquid.
Warning! Charge A/C System with Freon as Vapor, not Liquid!
If a charging hose is long enough you might get away with using liquid refrigerant because the liquid will partially change to a gas in the hose. The odds are not in your favor. More often you will freeze and shatter the compressors valves when the refrigerant hits the valves as a liquid. This happens in mere seconds, which is why we recommend charging the A/C system with the engine off. It is a sign of AC ignorance if a mechanic insists on charging a system with the vehicle running and the compressor turned on. A simple question to test a mechanics knowledge is "Do you charge the system with the car running?". If the answer is yes, RUN AWAY!!