air conditioner question
As stated above, an A/C unit doesn't need a neutral, just the 2 hots.
The nameplate usually states a minimum circuit ampacity. This determines the wire size. It also states a maximum breaker or fuse size. The wire size is usually 'too small' for the breaker, but perfectly legal and safe.
The reason is because the A/C unit is self-protected against overloads, so it cannot overload the wire. It can however, develop a short-circuit. This is the sole function of the breaker; to protect against short-circuits and ground faults.
The reason the breaker needs to be larger than normal is because the compressor contains a motor. All motors draw much more current when starting than they do when running. (Usually about 6 times as much). A 'normal' size breaker might see this starting surge current as a fault and trip when there isn't a problem.
About the only places that a breaker can be larger than the wire is A/C units, motors, and welders. There are a few others, but you'll never find them in residential wiring.