If it has that option there will be a switch that says rain sensor override or shutoff.
Fantastic fan rain sensor override.
If yours doesnt work that way and youre still under warranty have newmar fix it.
Depends upon the model.
Below are four photos showing how to disable the rain sensor.
If out of warranty call fantastic fan.
Realizing that the fantastic fans are basically worthless because the rain sensor overrides the fan operation i disabled all three fan rain sensors by cutting the wires running from the rain sensor to the fan circuit board.
Push and hold the up down button again red light goes out sensor is reenabled.
The simple reverse switch changes the direction of the fan blades drawing air in or out of the vehicle.
Here are some generic instructions.
Now all fans are working properly.
Push and hold the up down button for a few seconds red light comes on rain sensor disabled.