Low-pressure alarms in chillers indicate refrigerant pressure in the evaporator has dropped below safe thresholds, risking compressor damage. Below is a structured breakdown of causes, diagnostics, and solutions:
Refrigerant Shortage
Leaks (most common): In evaporator coils, valves, joints, or schrader cores.
Inadequate Charge: Underfilled during maintenance.
Evaporator Issues
Low Water Flow: Clogged strainers, failing pumps, closed valves, or air-bound pipes.
Fouled Tubes: Scale/slime buildup reducing heat transfer.
Low Load: Demand drops below chiller’s minimum capacity (e.g., at night/winter).
Component Failures
Stuck/Defective Expansion Valve: Restricts refrigerant flow into evaporator.
Clogged Filter-Drier: Blocks refrigerant movement.
Faulty Pressure Transducer: False readings triggering alarms.
Cold Weather Effects
Low Ambient Temps: Oversized chillers struggle to maintain pressure in winter.
Refrigerant Migration: Liquid refrigerant pools in cold condenser, starving evaporator.
Control Problems
Incorrect Chiller Setpoints: Overly aggressive suction pressure targets.
Failed Unloaders: Compressor unable to reduce capacity.
| Symptom | Diagnostic Checks | Solutions |
|---|---|---|
| Refrigerant leak | • Check oil spots, hissing sounds • Use electronic leak detector • Measure subcooling/superheat |
• Repair leak • Recharge to OEM specs |
| Low water flow | • Verify pump operation • Inspect strainers/valves • Check ΔP across evaporator |
• Clean strainers/pipes • Bleed air • Adjust VFDs |
| Fouled evaporator | High ΔT (>10°F/5.5°C) water in/out | • Chemically clean tubes • Improve water treatment |
| Expansion valve failure | Frost on valve body • Low superheat |
• Replace valve • Adjust superheat (typically 8-12°F) |
| Winter operation issues | Pressure drop during cold snaps | • Install suction accumulator • Use crankcase heater • Lower condenser fan speed |
Compressor Destruction: Low pressure → low refrigerant density → insufficient oil return → bearing seizure.
Floodback: Liquid refrigerant slugs into compressor, causing hydraulic shock.
Coil Freezing: Evaporator temperatures drop below 32°F (0°C), freezing water inside tubes.
Head Pressure Control:
Use fan cycling or variable speed drives to maintain condenser pressure.
Crankcase Heaters:
Prevent refrigerant migration into compressor oil during shutdown.
Suction Line Accumulators:
Capture liquid refrigerant before reaching compressor.
Weekly Checks: Log suction pressure, superheat, water ΔT.
Leak Tests: Quarterly electronic leak detection.
Water Treatment: Monthly testing to prevent scaling/biofilms.
Calibration: Verify pressure sensors annually.
Name: Tekin Cooling Co., Ltd
WhatsApp/phone: +8618875909946
WhatsApp/phone: +8618823849501
Email: info@tekincooling.com