20 amp service and A/C use

[TerraYacht]

I have a plug in watt meter that reads voltage, something like this one at Amazon: Amazon.com: P3 International P4460 Kill A Watt EZ Electricity Usage Monitor: Home Improvement

and my surge protector will disconnect if the voltage goes too low. The watt meter is ore convenient because you can just plug it in and leave it there instead of using a DVM.

Circuit breakers have a published curve: a 20 amp may let 30 or 40 amps through for a short time, then the 20 amp can be regarded as steady-state protection.

BTW, circuit breakers do get "tired" if they are used a lot, and will tend to open at a lower current than original. If the voltage looks good and the breaker still opens then try replacing it.