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The post mentions 30 amp and 20 amp.
Since an air conditioner, I suspect it requires a 240 volt, 20 amp circuit.
If that is the case, you would need 12/2 with ground for the air conditioner receptacle and a 20 amp double pole breaker.
#12 is only good for 20 amps, 30 amps requires #10 wire.
Let me know anything further needed or clarifications