The reason a 2000 watt generator won't run a 13,500 btu ac is that the ac draws about 2,000 to 2,100 watts (give or take a few) to start the compressor. This is close enough to the limit that manufacturing variations are enough that most generators and ace won't work but every now and then there will be one that will. Sort of a downhill-with-a-tailwind deal. But a 5,000 or 8,000 btu ac should work. Just don't count on being able to run anything else at the same time.