Frigidaire 12000 BTU A/C window unit

The reason that it's doing that is b/c at first its running only with the fan butwhen the compressor clicks on it trips the breaker if you have other items running off that circuit "unplug them" [even turned off items can still consume some power]. Then try to running only the ac unit see if it works a 12000btu takes a lot to run, if this doesn't work the ac may be to much for your circuit to handle and a smaller unit may be needed.