When you install a split receptacle, you should mount it upside down—that is, with the ground pin facing up instead of down. This is a precaution that alerts anyone using the outlet to the fact that it's a split receptacle and not a conventional duplex receptacle Wiring for a Split Rec...
Voltage drop means that though it may have measured 120v at the main box, it may now be only 115v – or possibly even 110v at the receptacle in a bedroom at the other end of the house, for example. The circuit for an AC unit, which traveled all the way through your house to the...