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Expansion Valve Blocked — Orifice Obstruction

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. Emergency: warm cloth on TXV body to thaw moisture freeze
  2. Root: recover → clean TXV or replace
  3. Replace drier concurrently
  4. Vacuum ≤500 micron for 30+ min
  5. Verify oil-refrigerant compatibility

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FAQ

What causes expansion valve blocked — orifice obstruction?

Moisture freezing in orifice Debris — copper chips, flux, oxides Wax deposition — improper oil/refrigerant pair Filter mesh blockage (50 micron) Saturated drier passes moisture downstream

How do I diagnose expansion valve blocked — orifice obstruction on site?

LP pressure 1–3 bar below normal Suction superheat abnormally high (15–25°C vs normal 4–8°C) TXV in/out ΔT ≥10°C (normal 1–3°C) Frost/condensation on TXV body Sight glass full liquid but evap empty

How do I fix expansion valve blocked — orifice obstruction?

Emergency: warm cloth on TXV body to thaw moisture freeze Root: recover → clean TXV or replace Replace drier concurrently Vacuum ≤500 micron for 30+ min Verify oil-refrigerant compatibility

What happens if expansion valve blocked — orifice obstruction is left unrepaired?

Refrigerant supply cut → evaporator starvation LP trip → restart → trip (short-cycling) Suction superheat >15°C → motor cooling fails Long short-cycling → winding overheating → motor burn-out risk Refrigeration capacity dropped to 0–30%

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