TX valve = Thermostatic eXpansion Valve
Yep, it's the refrigerant metering device.
Very simply it has a feeler bulb strapped to the outlet of the evaporator, a capillary tube back to a power element which is a diaphragm above the valve and inside this tiny, closed system is a measured refrigerant charge.
As the temperature changes at the evap outlet the pressure inside the power element alters and the diaphragm moves, which opens and closes, or more precisely modulates an orifice.
The high pressure liquid from the condenser is metered through this orifice into the evaporator.
There are other devices that can be used, eg. a fixed orifice, or domestic fridges use a length of capillary tube ( a copper tube with a tiny bore) with a precisely measured refrigerant charge, and larger systems can use electronic valves, low side floats, etc.

