TXV Stuck Open — Overfeeding Causes Liquid Slugging
A field reference for thermostatic expansion valve (txv) faults — what causes it, how to confirm it on the unit, how to repair it, and what fails next if you leave it. Written for working HVAC & refrigeration technicians.
How to confirm it on site
- Suction superheat 0–2°C
- Suction line surface frost/heavy condensation
- Liquid trace in suction line
- TXV ΔT < normal
- Discharge temperature lower than normal
Root causes
- Superheat setting too low
- Sensing bulb fell off suction line
- Diaphragm corrosion — opens biased
- Needle wear — incomplete close
- Bulb mounted on wrong line
If you leave it unrepaired
- Overfeeding → unevaporated liquid to compressor
- Liquid slugging → discharge valve break, piston/conrod damage
- Suction superheat 0–2°C (normal 4–8°C)
- Suction line frosting/condensation
- Long-term: compressor burn-out or mechanical failure
How to fix it
- Verify bulb position/insulation
- Adjust superheat to 4–8°C (CCW 1/4 turn = +1–2°C)
- Reinforce bulb insulation
- Replace TXV + drier if body damaged
- Prevention: install suction accumulator
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What causes txv stuck open — overfeeding causes liquid slugging?
Superheat setting too low Sensing bulb fell off suction line Diaphragm corrosion — opens biased Needle wear — incomplete close Bulb mounted on wrong line
How do I diagnose txv stuck open — overfeeding causes liquid slugging on site?
Suction superheat 0–2°C Suction line surface frost/heavy condensation Liquid trace in suction line TXV ΔT < normal Discharge temperature lower than normal
How do I fix txv stuck open — overfeeding causes liquid slugging?
Verify bulb position/insulation Adjust superheat to 4–8°C (CCW 1/4 turn = +1–2°C) Reinforce bulb insulation Replace TXV + drier if body damaged Prevention: install suction accumulator
What happens if txv stuck open — overfeeding causes liquid slugging is left unrepaired?
Overfeeding → unevaporated liquid to compressor Liquid slugging → discharge valve break, piston/conrod damage Suction superheat 0–2°C (normal 4–8°C) Suction line frosting/condensation Long-term: compressor burn-out or mechanical failure