Can you buy a new one?
Because your TXV has an equalizing line, there is no good way to really test it outside of a functioning system.
The equalizer line feeds vapor refrigerant pressure to the underside of the diaphragm. The bulb contains an external self contained refrigerant charge, which is used as a signal to feed pressure to the top.
Changes to the bulb temp influence the diaphragm direction, and the orifice metering size.
This is why the bulb must be placed upstream from the equalizing line fitting attachment on the evaporator.
The pressures above and below the diaphragm need to be pretty equal, with only small temp changes at the bulb being what ultimately controls the orifice size change.
But the equalizing line is also indirectly connected to the TXV outlet liquid line side, and so because these are technically connected, it is a bad idea to use water to flow through the TXV for testing.
No good way to really test em outside of a functioning, closed and properly charged system unfortunately
Usually what happens, is the bulb loses its charge over time, and TXV fails in fully open, which means liquid refrigerant entering the evaporator is not subject to an optimal pressure drop, resulting in ineffective cooling even though the evaporator might be flooded and evaporation is actually taking place.
The pressure/temperature relationship of refrigerants is a special one, and the TXV controls the optimal pressure drop of liquid entering the evaporator
A specific pressure drop AND a good supply of liquid refrigerant to flood the evaporator are both needed for good heat exchange to take place during evaporation from a liquid to a gas.
