When a Fujitsu air conditioner's indicator lights flash alternating red and green patterns, it typically indicates an active communication error or transmission fault between the indoor air handler and the outdoor condenser unit. This can be caused by temporary power surges, loose low-voltage control wiring at the terminal blocks, or environmental damage to the interconnection cables. To troubleshoot, perform a hard power reset by shutting off the main breaker for ten minutes. If the alternating red and green flashing immediately returns upon startup, a qualified technician must inspect the wiring and control boards.
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