My experience comes from working maintenance at a wastewater treatment plant. A WW plant and collection system uses all sizes of generators to power mainly power pumps. This is what I learned from working with engineers : an alternating electric motor draws up to 8 times its full load amps (fla) on start up. A resistive load such as an electric heater will pull the same amps whether its on start up or not. So when buying a generator first determine how much load will be used to power motors ( find a motor face plate for this data, call someone in hvac sales, whatever) and how much will be resistive(lights,stove,whatever). Convert all amps to watts (multiply amps by the voltage used(120v,22ov). Next to to keep from overloading the system add 15% of load watts to the load figure.You've just sized your generator.
Two things about air conditioners :
1. for example a 3 ton unit may normally run on 15 to 25 amps(it all
depends on its efficiency and the amount of load its facing. Again
for example if it ran on 15 amps then 15 amps x 220 volts x 8 =
26400 watts. Actually I have heard on ac's being run on a lot less,
but what Ive told you is what engineers use.
2. Bear in mind that I'm not good at describing this but I'm trying to
give you enough background to ask questions. Here goes.
Generators made for home use may or may not be center tapped.