If your coach has a Surge Guard protected transfer switch, one that looks for open neutral, open ground, etc, it may not allow the hookup as you will not have a neutral with your 3 wire connection. i have an outside 3 wire, 120v RV receptacle that I wired straight off my house breaker panel and I can run one A/C in the MH that way. It has one hot, one neutral and one ground. Standard Rv 30a receptacle.