Metering Devices

TXV operation and superheat control, fixed-orifice pistons, bulb charge, hunting and restriction diagnosis.

5 guides

• Diagnosing a Refrigerant Restriction (Drier and Liquid Line)
  How to identify a partial refrigerant restriction in the liquid line or filter-drier using a temperature drop across the component, plus the subcooling/superheat signature that separates a restriction from a low charge.
• Fixed Orifice (Piston) vs TXV: How They Differ in the Field
  The practical differences between a fixed-orifice piston and a thermostatic expansion valve — how each meters refrigerant, how charging differs, and how each behaves when conditions change.
• How a TXV Controls Superheat
  How a thermostatic expansion valve modulates refrigerant flow to hold evaporator superheat in a tight band, the three forces acting on the diaphragm, and why it self-corrects to load changes.
• Is My TXV Hunting or Stuck? Reading the Symptoms
  How to tell a hunting TXV from a stuck-open or stuck-closed valve using superheat behavior over time, suction pressure, and frost patterns, plus what each failure mode looks like in the field.
• TXV Bulb Charges and Equalizer Types Explained
  What the different TXV bulb charges (liquid, gas/MOP, cross) do, the difference between internal and external equalizers, and why the valve has to match the refrigerant it's metering.

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