What happens
Valve operation and system conditions create excess or oscillating feed.
Typical symptoms
Unstable readings or possible liquid return to the compressor.
Checks that distinguish this cause
Evaluate load stability, airflow, bulb installation, valve selection and adjustment history before modifying settings. Follow the valve-specific diagnostic process.
What can look similar
Ice buildup or overcharge can contribute to liquid return without a defective valve.
Repair direction
Correct the established system condition or valve fault using the approved procedure.
Verify the repair
Verify stable operation and appropriate compressor return conditions.
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
This cause is a reference topic; it does not yet have a dedicated simulated call. Browse the practice board.
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.