NEC code says that dedicated appliances can't draw more than a certain % of rated load for wire or breaker. I think it's like 80%. So for a 15A breaker, max load shouldn't exceed about 12A. Most of the non high efficiency 13.5K units have a max draw near 12-14A, so 15A is IMHO marginal. And once a breaker starts tripping, it will eventually trip at below the rated current.
A quick check on the coleman site says the MachIII has a rated running current of 13.1A. standard draw is listed at 1400W and desert conditions listed at 1700W. 1700W is over the limit for a 15A breaker. That would be 14A or so draw, well in excess of NEC code for a dedicated appliance on a 15A circuit.
And AC draw is dependent on temperature as well, going up as temps go up. It may draw only 10A or so on a cool day but 14+ on a hot day.
Now if you go to a 20A breaker MAKE SURE THE WIRING IS 12GA, not 14GA!!!!! 14GA wire is only rated for use on a 15A or lower breaker.
