Scroll Chillers Critical Interlock

York YLAA Scroll Chiller Alarm B2: Compressor Motor Overload

Published: 2026-05-08

🚨 Critical Diagnostic Alert

Alarm B2 on the York YLAA air-cooled scroll chiller indicates that a compressor motor overload relay has tripped, disconnecting power to the affected compressor. Unlike auto-reset high/low pressure alarms on the YLAA, the B2 alarm is manual reset only — this is a deliberate design choice to force a technician to investigate the root cause before the compressor can restart.

York YLAA chillers use Copeland scroll compressors with internal motor protection (embedded thermistors) AND external overload relays — providing two independent layers of motor protection. If only the external overload relay tripped and the internal thermistors did not, the overload relay may be misadjusted or failing rather than the compressor being at fault. Always check relay calibration before condemning the compressor.

🔍 Symptoms Checklist

⚠️ Specific compressor contactor trips on overload relay
⚠️ Compressor motor draws >125% RLA before trip
⚠️ Overload relay is hot to touch after trip
⚠️ Alarm is manual reset — will not auto-restart

🛠️ OEM Replacement Parts

Part Name	OEM Part Number	Est. Price
Compressor Overload Relay (Class 10)	`YK-OLR-010`	$145
Compressor Contactor (3-Pole, 50A with Aux)	`YK-CONT50`	$185
Run Capacitor Bank (set of 3, 60 μF each)	`YK-CAP-BANK3`	$240

📋 Interactive Diagnostic Procedure

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

1 Measure Running Amps & Voltage Balance

Before assuming compressor failure, check the electrical supply. Measure each leg's running amps (all three should be within 10% of each other) and voltage (phase-to-phase, all three within 2% of each other). A 2% voltage imbalance can cause a 10-15% current imbalance. A voltage imbalance >3% requires correction at the building electrical panel before any further compressor diagnostics — the compressor is not the problem, the power supply is.

2 Verify Overload Relay Trip Class & Setting

York YLAA chillers use IEC Class 10 overload relays (trip within 10 seconds at 600% FLA). Verify the relay's amp setting matches the compressor nameplate RLA. A common field error: the overload relay was set to the wrong value after a previous compressor replacement (e.g., a 25-ton compressor installed where a 20-ton was, but the overload relay setting wasn't updated). Check and adjust the dial to match the installed compressor's RLA.

3 Megger Test the Compressor Motor Windings

Disconnect all compressor leads at the contactor and overload relay. Perform a 500V DC megger test: phase-to-phase and each phase-to-ground. Acceptable: >100 MΩ phase-to-ground, >50 MΩ phase-to-phase at 68°F. Borderline: 20-100 MΩ (motor can run but will have elevated leakage current that heats windings). Failed: <20 MΩ (replace compressor). For compressors in the borderline range, perform an acid test on the oil — high acid number indicates internal motor insulation breakdown into the oil.

4 Inspect Contactor for Single-Phasing

A burned contact on one pole of the 3-pole contactor creates a single-phase condition — the compressor motor tries to run on two phases, draws locked-rotor current, and trips the overload. Signs of single-phasing: that specific compressor contact is visibly burned/eroded compared to the other two, a humming sound from the compressor without rotation (before overload trip), and the overload trips within 2-5 seconds of contactor closure. Replace the contactor as a complete assembly — replacing individual contacts is unreliable.

🔗 Related Error Codes — Scroll Chillers

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

Scroll Chillers Critical Interlock

⚡ Fault-Induced Energy Waste Estimator

When HVAC equipment runs with active error codes, it operates inefficiently and wastes electricity. Estimate the monthly cost of delaying repairs. All calculations run locally in your browser.

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References & Industry Standards

ASHRAE 15 — Safety Standard for Refrigeration Systems
ASHRAE 34 — Refrigerant Designation & Safety Classification
AHRI 550/590 — Water-Chilling & Heat Pump Packages
SMACNA — HVAC Duct Construction Standards
Manufacturer Service Manuals — Carrier, Trane, York, Daikin, Lennox

York YLAA Scroll Chiller Alarm B2: Compressor Motor Overload

🔍 Symptoms Checklist

🛠️ OEM Replacement Parts

📋 Interactive Diagnostic Procedure

🔗 Related Error Codes — Scroll Chillers

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Trane CGAM Alarm HPC: High Pressure Cutout — Circuit Protective Trip

York YLAA Scroll Chiller Alarm B5: Phase Loss / Phase Reversal Protection

Daikin McQuay AGZ Alarm E3: Compressor Motor Overload — Thermal Trip

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⚡ Fault-Induced Energy Waste Estimator

References & Industry Standards