What a TXV does in an HVAC system
A TXV, or thermostatic expansion valve, controls how much refrigerant flows into the evaporator coil by reading conditions at the coil's outlet and adjusting the valve opening to match. It sits between the high-pressure and low-pressure sides of the refrigerant circuit. A fixed orifice passes a set amount regardless of load; the TXV reads actual demand and responds to it.
What does a TXV do in an HVAC system?
A thermostatic expansion valve, or TXV, sits at the inlet of the evaporator coil, right where refrigerant moves from the high-pressure side of the circuit to the low-pressure side.
Its job is to meter how much refrigerant enters the coil. It does this by reading conditions at the coil's outlet, specifically how much heat the refrigerant has absorbed by the time it reaches that point. When the coil is absorbing a lot of heat, the valve opens wider to let more refrigerant through. When demand drops, it closes down. A fixed orifice passes the same amount of refrigerant regardless of what the system actually needs. The TXV matches supply to demand in real time, which keeps the evaporator working efficiently across a wide range of conditions rather than being tuned for just one.
How do you know if your TXV is failing?
Frost on the refrigerant lines or the evaporator coil is one sign worth watching.
So is uneven cooling from room to room, or a system that runs without ever satisfying the thermostat. Those symptoms point toward the TXV, but they do not confirm it. Low refrigerant charge produces the same frost. A failing compressor produces the same endless runtime. A dirty evaporator coil restricts airflow in ways that look identical from the supply vents. Separating these causes requires gauge readings on the high and low sides of the refrigerant circuit, along with temperature measurements at specific points a homeowner cannot safely reach. That kind of diagnosis is a measurement made with instruments, not an observation made from the living room.
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