the Glacier Bay system is unique in that it cycles the use of the compressor through a 4 port manifold: freezer plate, refrig plate, forward air con, saloon air con, in that order of priority. Only one active at once. After the freezer and frig plates are frozen, you can run either the forward cabin air or the saloon air. The evap units are not ducted, but built into the cabinetry (they are only about 12X 10 x 10 inches and weigh maybe 8 lbs). Draw of the compressor while it is running is about 20 amps. The capacity for air con is only about 5000 btu, certainly not overkill for the saloon. It does dehumidify very well, in fact this is its main problem. So much water is pulled out of the air (on humid days in the Great Lakes) that drops blow out of the unit and onto the woodwork/upholstery. I am still grappling with that - it does have a condensation pan and drain, but if its real humid it blows off the evaporator before it drains. Like Dan says, even without a great temperature drop, the dehumidification makes it considerably more comfortable, and that is noticeable within 15 minutes of turning it on.