A blinking or flashing indicator light on a Fujitsu Halcyon indoor air handler usually signals that the system's self-diagnostic control board has detected a specific operational anomaly, safety lockout, or maintenance reminder. Common reasons for flashing lights include a dirty air filter that requires cleaning, a full condensate drainage pan triggering an overflow safety switch, or an electrical communication error between the indoor unit and the outdoor condenser. To diagnose the exact issue, check the error code flashing sequence or use the wired remote controller to pull the detailed error history, then perform a power reset or contact a certified technician if the fault persists.
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