If it has that option there will be a switch that says rain sensor override or shutoff.
Fantastic fan rain sensor override.
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.
Some do and some do not.
Here are some generic instructions.
The powerful yet compact dometic fan tastic vent model 7350 has automatic variable speeds to get the airflow precisely as you want.
If out of warranty call fantastic fan.
Push and hold the up down button for a few seconds red light comes on rain sensor disabled.
Push and hold the up down button again red light goes out sensor is reenabled.
If yours doesnt work that way and youre still under warranty have newmar fix it.
Depends upon the model.
Now all fans are working properly.