Code A0: External protection device activated
Issue Description & Safety Warning
The Daikin SM-TS3 HVAC Self-Diagnosis has triggered a critical External protection device activated alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Unit area: Indoor Unit Product scope: RA, SkyAir, VRV, Package, Heat reclaim ventilator, Chiller, Fan Coil Chart object marker: kkk Supposed causes: - External protection device connected to the terminal strip - T1-T2 of indoor unit is activated
Source: Daikin SM-TS3 Simple Self-Diagnosis by Malfunction Code chart
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Daikin SM-TS3 HVAC Self-Diagnosis Alarms
Daikin controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code A0 on the SM-TS3 HVAC Self-Diagnosis identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Daikin's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 139 Daikin SM-TS3 HVAC Self-Diagnosis codes.
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