What happens
A restriction limits liquid delivery to the evaporator.
Typical symptoms
Reduced capacity and a starved-evaporator pattern under known conditions.
Checks that distinguish this cause
Verify liquid availability, airflow, superheat and subcooling using the model procedure. Compare conditions along the liquid path to localize a restriction before replacing the valve.
What can look similar
Insufficient charge can also starve the evaporator; a valve cannot feed liquid it is not receiving.
Repair direction
Correct the proven restricted component using the approved clean-system and replacement procedure.
Verify the repair
Confirm stable refrigerant feed and model-appropriate operating measurements.
Equipment-specific limits
Identify TXV, fixed orifice or electronic expansion valve. Do not use TXV adjustment as a shortcut around airflow, charge or liquid-supply faults.
Practice this diagnosis
These simulated calls exercise this component or repair family. The article describes a broader diagnostic process; a call may represent a different cause within that family.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- Parker Sporlan: Thermostatic expansion valves — Bulletin 10-10TXV operation and application; select the bulletin for the installed valve.
Editorial review: 2026-09-29. Verify the current manual for the installed model.