The TXV (Thermal Expansion Valve) — sometimes called TEV or expansion valve — is a precision metering device that regulates how much refrigerant flows into the evaporator coil based on the cooling load at any given moment. It’s what allows modern AC systems to maintain proper superheat across a wide range of operating conditions.
TXV vs. older “piston” metering
Older AC systems used a fixed-orifice piston instead of a TXV. The piston worked at one specific design condition but lost efficiency at any other temperature. TXVs dynamically adjust, which is why they’re required for 14+ SEER2 systems by federal code.
Common TXV problems
- Stuck-open (overfeeds refrigerant, causing liquid floodback to compressor)
- Stuck-closed (starves the coil, causing freeze-ups)
- Contaminated by moisture or debris
- Failed sensor bulb (loses control feedback)
TXV replacement is a moderate repair requiring refrigerant recovery, brazing in the new valve, vacuum, and recharging — typically $500-$900 including parts and labor.
Related: Evaporator Coil, Refrigerant, Superheat.
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Right Way Mechanical is a family-owned HVAC contractor serving Wheat Ridge, Arvada, west Denver, and the Colorado foothills.