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TXV Stuck Closed — Diaphragm/Needle Frozen

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.

Thermostatic Expansion Valve (TXV)

How to confirm it on site

Root causes

If you leave it unrepaired

How to fix it

  1. Check sensing bulb first — replace bulb+capillary if leak
  2. Diaphragm rupture: replace valve body
  3. Replace drier + vacuum
  4. Verify bulb position (12 or 4 o'clock on suction line)
  5. Insulate bulb from ambient

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FAQ

What causes txv stuck closed — diaphragm/needle frozen?

Sensing bulb refrigerant loss → diaphragm pressure 0 Diaphragm rupture/crack Spring permanent deformation Needle/seat corrosion Debris blocks needle action

How do I diagnose txv stuck closed — diaphragm/needle frozen on site?

Sensing bulb test — bulb cooling causes no response TXV warming test — no opening action TXV inlet warm/normal, outlet still liquid (no evaporation) Suction superheat very high (>20°C)

How do I fix txv stuck closed — diaphragm/needle frozen?

Check sensing bulb first — replace bulb+capillary if leak Diaphragm rupture: replace valve body Replace drier + vacuum Verify bulb position (12 or 4 o'clock on suction line) Insulate bulb from ambient

What happens if txv stuck closed — diaphragm/needle frozen is left unrepaired?

Diaphragm fails → needle stuck closed → no refrigerant Same as blocked: LP trip, short-cycling, zero capacity Liquid backup in liquid line → HP trip possible Compressor starved → motor cooling failure System shutdown via compressor protection

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