R-Pro › Field cases › Chillers

Unable to Reach Process Temperature — Chiller Setpoint Not Achieved

Likely causes

Reduced chilled water flow — Y-strainer clog, air lock, or pump failure

Check: Measure evaporator chilled water ΔT — flow insufficient if >8°C (normal 5–8°C). Y-strainer clogged if differential pressure exceeds 50 kPa

What to do: Clean Y-strainer → purge air by opening air vents → replace pump impeller if current drops 15%+ below rated

Low or overcharged refrigerant

Check: Check sight glass for bubbles (undercharge) or measure subcooling with gauge (overcharge if subcooling >15°C). Confirm R-134a high-side normal range: 14–16 bar

What to do: Undercharge: repair leak then charge to spec. Overcharge: recover excess with recovery machine and readjust

Screw compressor slide valve stuck

Check: Check if capacity indicator is stuck at 50% or 100% without change. Run oil pump and manually toggle solenoid ON/OFF — no position change confirms stuck valve

What to do: Oil sample: replace immediately if TAN >0.5 mgKOH/g or viscosity deviates >±10% from ISO VG 68 → replace oil filter simultaneously → inspect/repair slide valve hydraulic circuit

Insufficient antifreeze concentration or temperature sensor error

Check: Measure antifreeze concentration on-site with refractometer (within 5 min). Cross-check temperature sensor against reference thermometer — replace if deviation exceeds 1°C

What to do: Add antifreeze concentrate immediately if below 30% (EG 30% = -16°C freeze point). Calibrate or replace temperature sensor

Field tip

'50% Rule': consider replacement if repair cost >50% of new unit, age 12–15+ years, and R-22 refrigerant. Chilled water ΔT >8°C is the first diagnostic indicator.

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