What happens
Poor sensing contact or an incorrect pressure-reference path makes the valve respond to the wrong conditions.
Typical symptoms
Unstable or inappropriate refrigerant feed despite apparently adequate liquid supply.
Checks that distinguish this cause
Inspect the isolated bulb location, contact, insulation requirements and equalizer connection against the valve and equipment instructions.
What can look similar
Low load and unstable airflow can cause similar behavior without a sensing installation fault.
Repair direction
Correct the approved sensing and equalizer installation, or replace a confirmed damaged assembly.
Verify the repair
Verify controlled superheat at stable load using the correct refrigerant convention.
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.