Chiller High Pressure (HP) Trip — Compressor Shutdown

Question

Accepted Answer

Dirty condenser — air-cooled: dust/insects, water-cooled: scale/biofilm. Check: Air-cooled: visually inspect coil fins (pollen, leaves, insects); high gauge rising (R-134a normal 14–16 bar, >18 bar = fouled). Water-cooled: inlet/outlet water ΔT (normal 5°C, dropping below 3°C indicates tube fouling); shell side hot to the touch What to do: Air-cooled: cut power → remove coil guard → wash top-down with low-pressure water (15–20 bar) + straighten fins with comb + alkaline cleaner if heavy. Water-cooled: stop water circulation → remove end covers of condenser → brush clean tubes mechanically or circulate acid descaler for 4–8 hrs → neutralize rinse → restart. Annual cleaning required Condenser fan stopped or reversed rotation (air-cooled). Check: Visually verify fan rotation — air should discharge upward; if stopped, measure capacitor (±10% of label). For 3-phase, check phase sequence (reversed phase = reverse rotation). Measure fan motor winding resistance (balanced between phases) What to do: Bad capacitor → replace with same μF/voltage. Reverse rotation → swap any two phases (e.g., L1 and L2). Motor burnt out (smoke/burn smell) → replace with same kW/pole. Check fan blade for deformation/damage Low cooling water flow (pump failure, Y-strainer clogged, valve closed). Check: Check pump discharge pressure gauge (±10% of design), Y-strainer differential pressure (>0.3 bar = clogged), verify valves visually open. If flowmeter present, check % of design flow. Also verify cooling tower sump level (evaporation/drift loss) What to do: Disassemble and clean Y-strainer (discard debris); fully open valves; if pump failed, inspect impeller/seal and replace pump if needed. Bleed air via air vent. If tower sump low, check makeup water line and float valve Refrigerant overcharge. Check: Measure subcooling — liquid line temp minus condensing saturation temp. Normal 5–8°C; >10°C = overcharge. Also accompanied by high discharge pressure and completely clear liquid sight glass (no bubbles at all). Check service history for top-offs What to do: Recover excess from high side with recovery machine — liquid recovery is faster. Monitor subcooling and high pressure in real time during recovery; stop when subcooling returns to 5–8°C. Record amount recovered. Finally weigh total charge vs. nameplate Non-condensable gas (air or residual nitrogen) in system. Check: Shut down for 30+ min to stabilize → measure ambient at condenser → compare with high-side gauge's saturation temperature. If saturation >5°C above ambient, non-condensables present. Suspect inadequate evacuation in past service What to do: Full recovery → evacuate with vacuum pump to ≤500 micron for 30+ min → perform vacuum hold test (rise ≤100 micron in 15 min) → weigh-in exact nameplate charge. Use fresh vacuum pump oil and high-quality vacuum hoses

Chiller High Pressure (HP) Trip — Compressor Shutdown

Likely causes

Dirty condenser — air-cooled: dust/insects, water-cooled: scale/biofilm

Condenser fan stopped or reversed rotation (air-cooled)

Low cooling water flow (pump failure, Y-strainer clogged, valve closed)

Refrigerant overcharge

Non-condensable gas (air or residual nitrogen) in system

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