Our MH has a basement HVCA and in our installation that switch lets the HVAC work on 30A or 50A. 30A uses a single stage compressor as opposed to the 50A setting which has full compressor. This effects the amount of cooling the HVAC can accomplish and also the drain on the shore power connection. I've use the 30A setting when visiting friends and connected to a 30A house circuit.
J.J. Hayden (KN4SH)
2005 National Dolphin 5342