Centrifugal Chillers Critical Shutdown

Daikin WSC Centrifugal Chiller Alarm A07: High Motor Winding Temperature

Published: 2026-06-24

🚨 Critical Diagnostic Alert

Alarm A07 on a Daikin WSC centrifugal chiller indicates that the motor winding temperature sensor has detected a temperature exceeding the safe operating limit — typically 248°F (120°C) for standard semi-hermetic motors or 212°F (100°C) for inverter-duty motors. This is a critical shutdown alarm: the chiller will not restart until the motor temperature drops below the reset threshold and the alarm is manually cleared.

The most common root cause is insufficient motor cooling refrigerant flow. Daikin WSC chillers use liquid refrigerant from the condenser to cool the motor windings. If the motor cooling circuit is restricted — by a clogged filter-drier, a failed expansion valve, or low system charge — motor temperature rises rapidly within the first 30-60 minutes of operation. The second most common cause is high motor load combined with marginal cooling: if the chiller is operating at 100% FLA in a high-ambient condition, the motor cooling circuit may be undersized for the actual operating point.

🔍 Symptoms Checklist

⚠️ Chiller trips on high motor temperature
⚠️ Motor winding resistance reading elevated
⚠️ Possible refrigerant odor near motor housing
⚠️ Control panel displays A07 alarm

🛠️ OEM Replacement Parts

Part Name	OEM Part Number	Est. Price
Motor Winding Temperature Sensor (PTC Thermistor)	`DKN-5028-01`	$385
Motor Cooling Refrigerant Filter-Drier	`DKN-3319-07`	$120

📋 Interactive Diagnostic Procedure

Click each step to expand detailed diagnostic instructions. Follow in sequence — each step builds on the previous one.

1 Verify Motor Cooling Refrigerant Flow

Check the sight glass on the motor cooling line. Bubbles indicate insufficient refrigerant flow to the motor. Verify the motor cooling expansion valve is not stuck closed. Measure the temperature difference across the motor cooling solenoid — a delta T less than 5°F indicates the valve is not opening.

2 Check Motor Winding Resistance

Lock out and tag out power. Discharge capacitors. Measure winding resistance phase-to-phase at the motor terminal box. All three readings should be within 5% of each other. A deviation >10% indicates winding damage. Compare readings to factory baseline values in the motor test report.

3 Inspect Motor Cooling Filter-Drier

A clogged filter-drier restricts refrigerant flow to the motor. Measure the temperature drop across the drier — a drop >3°F indicates restriction. Replace the filter-drier core (DKN-3319-07). Always install a new filter-drier — do not attempt to clean and reuse.

4 Verify PTC Thermistor Operation

Disconnect the thermistor leads at the control panel. Measure resistance — at 77°F, the thermistor should read 100-1,000 ohms. An open circuit (infinite resistance) indicates a failed thermistor. If the thermistor has failed open, the controller reads this as an over-temperature condition and trips the chiller.

5 Test Run and Monitor

After repairs, restart the chiller in manual mode at minimum load. Monitor motor winding temperature on the Trend screen. Temperature should stabilize within 10 minutes below 212°F. If temperature continues to rise, the motor cooling circuit has insufficient capacity — check for refrigerant undercharge or non-condensables in the system.

🔗 Related Error Codes — Centrifugal Chillers

Other diagnostic guides in the same equipment category. Common failure patterns often share root causes — cross-referencing speeds up diagnosis.