Chiller Low Pressure (LP) Trip — Low Refrigerant or Expansion Valve Fault

Question

Accepted Answer

Refrigerant leak — shaft seal, flange, valve gasket. Check: Connect gauge manifold and check low-side pressure (R-134a normal: 3.5–4 bar; below spec suspects leak). Scan shaft seal, flanges, and service valves in order with electronic leak detector What to do: Repair leak → evacuate to ≤500 microns for 30+ min → recharge to spec using electronic scale Expansion valve (TXV/EEV) clogged or faulty. Check: Measure superheat with gauge — TXV clog suspected if >15°C vs normal 5–8°C. Check temperature differential across valve inlet/outlet What to do: Clean or replace TXV strainer → re-adjust superheat to 5–8°C. For EEV, check controller output signal (0–10V) and step count, then replace if faulty Filter drier clogged. Check: Measure temperature before and after filter drier — if outlet is 2°C+ colder than inlet, clogged. Check sight glass moisture indicator (yellow = wet, green = dry) What to do: Replace filter drier (after 1–2 years service or when moisture indicator saturates). Evacuate 30+ min after replacement → recharge Low pressure switch faulty. Check: Confirm actual low-side pressure with gauge and compare to trip setpoint — if actual pressure is normal but trip occurs, switch is faulty. Confirm with terminal short-circuit test What to do: Replace LP switch. Temporary operation after short-circuit test is possible but always investigate root cause simultaneously

Chiller Low Pressure (LP) Trip — Low Refrigerant or Expansion Valve Fault

Likely causes

Refrigerant leak — shaft seal, flange, valve gasket

Expansion valve (TXV/EEV) clogged or faulty

Filter drier clogged

Low pressure switch faulty

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