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Low Chilled Water Flow → Evaporator Freeze Protection Trip

Likely causes

Evaporator water-side strainer clogged — flow drops sharply when differential pressure exceeds 50 kPa

Check: Measure strainer differential pressure — clean immediately if >50 kPa. Evaporator ΔT >8°C confirms insufficient flow (normal 5–8°C)

What to do: Clean strainer (recommend periodic cleaning every 6 months) → verify flow recovery after cleaning → confirm ΔT returns to 5–8°C

Chilled water pump impeller wear or air entrainment

Check: Measure pump current — if more than 15% below rated, suspect impeller wear or air entrainment. Check pump outlet pressure

What to do: Open high-point air vents to remove air → replace impeller if flow does not recover. Install automatic air vent if air pockets recur

Motorized valve actuator malfunction — opening stuck below 30%

Check: Manually verify motorized valve opens to 100% — if opens manually, actuator is faulty. Measure valve control signal (4–20 mA) to confirm signal is normal

What to do: Replace actuator. Check for wire breakage and poor connections, then reconnect

Field tip

Evaporator ΔT below 6°C = excessive flow or sudden load drop; above 8°C = insufficient flow. Check both thresholds on-site immediately. Strainer ΔP 50 kPa = clean immediately.

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