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TXV Sensing Bulb Charge Loss — Capillary Crack or Leak

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. Replace bulb+capillary+diaphragm as assembly
  2. Match exact refrigerant type
  3. Route capillary along low-vibration path + spiral wrap
  4. Double-layer insulation on bulb

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FAQ

What causes txv sensing bulb charge loss — capillary crack or leak?

Capillary fatigue from vibration Capillary corrosion (saline/sulfur exposure) Bulb body corrosion/crack Joint leak — packing aged Natural charge loss after 10+ years

How do I diagnose txv sensing bulb charge loss — capillary crack or leak on site?

Bulb in liquid refrigerant — no TXV response Diaphragm cap pressure 0 or very low Capillary surface — fine cracks/corrosion under magnifier Bulb body damage

How do I fix txv sensing bulb charge loss — capillary crack or leak?

Replace bulb+capillary+diaphragm as assembly Match exact refrigerant type Route capillary along low-vibration path + spiral wrap Double-layer insulation on bulb

What happens if txv sensing bulb charge loss — capillary crack or leak is left unrepaired?

Bulb charge loss → diaphragm pressure 0 → valve closed Same as stuck closed: LP trip, short-cycling, zero capacity Initially partial operation → progressive failure Vibration accelerates capillary fatigue

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