A/C breaker trips whenever ambient temp is high?

The air conditioner does use more power at higher ambient temperatures. The breakers are also thermal trip devices (in general, for this situation--they also have a magnetic trip mode that's irrelevant here) and so when they are warmer they will trip a little sooner.

That's not to suggest that swapping the breaker is not a good idea; it's merely to give some reasons why it would trip when the temperature is higher but not when it's lower.