Don't know where it is on your boat, but I have a related problem with mine. The sensor on mine is located behind the intake grill work, so that it sees air temp coming from the living space and into the conditioning unit. The problem with this on 'heat', is it will run for awhile until the thermostat is satisfied, then shut off. By. then the AC unit is hot, and with no more air flow it heat soaks the cabinet, including the sensor. The room temp has to drop another 10 degrees or more before it comes on.
When you find the sensor, move it to the living space away from any of the inlet or outlet ducts.