Too much generalization here - need to get the facts and do the arithmetic that Happywanderer alluded to. Some microwaves do indeed use enough power that running them at the same time as an a/c will push the 30A limit. Especially if voltage is on the low side (a/c amp load goes up as voltage goes down). A 1000 watt microwave can easily pull 12-13 amps. That's mostly because the microwave watts listed are the output power and the input power is typically about 50% or more greater. For example, a GE Spacemaker 1000w microwave uses 1480 watts on input. Some 700 watt microwaves use as much as 1200 watts.
Combining 1200-1400 watts of microwave usage with another 1400+ for the a/c leaves very little for anything else when 3600 is the total max. People tend to ignore the other power uses that are out of sight and often on a thermostat, e.g. water heater, fridge (in 120vac mode). And the converter/charger is always on and using at least an amp or two.
