What is a TXV What? Basically in the flow of refrigerant and an AC system, a TXV is simply the metering device that meters the refrigerant before it goes through the evaporator coil it's needed because if it weren't there, the coil would not be able to cool. You would essentially have a compressor that was pulling liquid refrigerant all the way through the evaporator coil and back to the outdoor condensing unit. And so in the old days we used to have what we called Pistons a small mechanism in there that just simply had a small hole in it and that's what would meter the refrigerant. But As time was gone on, better technology came out and they started producing these TXV valves that could open and close based on the temperature that the valve was sensitive.