Using an autoformer epically with a 15 amp outlet will get you the click of darkness or a risk of a house call from a company that still does those (Fire Dept). Hopefully not the house call.
I would run it off a 20 amp outlet with at least 10ga wire if not 8ga wire. Let me do the calculations.
250 foot run is 500 feet round trip. Here are voltage drops figures for 10 amps of load, Most A/C's run a bit more than that.
10GA 1.6 volt (That should do it)
8GA .3141 (even better)
6ga .2 (Still better)
I rounded slightly
Information source
Powerstream dot com chart
