What would cause the A/C switch indicator light to keep flashing on and off?
Your AC's magnetic clutch relay could be bad, in the under hood fuse box it is labeled MG CLT (2nd from right, middle). In Toyota nomenclature it is part 90987-02028, a SPST 12-volt relay, you can test if this is the fault by temporarily swapping it with one of the other relays, such as the TOW or AF HEATER relays. The other problems that can cause the flashing AC indicator are the AC amplifier assembly or the compressor itself, but I'd swap the relay first.
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