One of the first things I learned about my Roadtrek was how to use the roof fan to provide ventilation. Being an old person who grew up in the south before universal air conditioning, I was familiar with the principle, because our house had such a fan. We called it the attic fan because it sucked the air in the house up into the attic. Even a kid like me could easily understand how to direct airflow by opening windows to let cool outside air into the house. Open the windows on the shady side, not the hot sunny side. Capitalize on existing outside airflow.
In addition to removing cooking smells and shower humidity, the fan also allows you to keep your inside temperature near the ambient temperature, instead of the runaway thermal event created by a closed vehicle in direct sunlight. A little practice is all it takes to figure out what the best fan speed and combination of open windows is to maintain a comfortable interior. Just make sure that you keep windows closed if they're near things like running generators, water heaters, and other sources of noxious fumes.
The fan also works great to suck any stray mosquitoes that snuck into your RV up onto the screen, along with whatever else is airborne inside your vehicle, which in our case is a fair amount of cat hair, plus greasy cooking aerosols, dust, etc. The unpleasant accumulation of bugs, hair, dirt, and grease on the screen means it has to come off once a week or so for cleaning. My old fan on my 2003 screwed on, a major pain, and it was quickly replaced by a snap-in screen I found online, and is sometimes sold in RV stores.
One thing about these snap-in screens, though – as delivered, they are a bear to get in and out, because the part of the tang that hooks over the lip is flat. It's a dicey proposition whether you break the plastic rim by pulling on it the wrong way before it comes loose. To solve this problem, I filed mine off to a wedge-shaped tang, and my screen pops in and out easily now. Here's a photo of the modified tang – the side nearest the screen used to be flat. Push slightly inward toward the center of the screen anywhere around the rim, and the tang will pop loose. Work your way around the rim, loosening one tang at a time, and it's an easy job.
One last thing – sometimes your fan won't come on, and you have checked the fuse and it's OK. If you have one of the new ones, the motor that opens and closes the lid works fine, just no fan. First thing to check is to see if you have accidentally turned the thermostat down so low that it's too cold where you are to get the fan to turn on. If that is OK, remove the screen and locate the switch that turns the fan off when the lid closes. It's on the front (hinged) side of the fan. Mine is on the driver's side. Just follow the wire, and there it will be.
Power from the fuse goes to the switch, and through it to the motor. It's just like a refrigerator door light switch – extended is on, compressed is off. Given the dirty environment it operates in and the low voltage it operates under, any minor particulate matter caught in this switch will cause it to fail to make contact. Press the switch and let it pop out a few times – that usually clears the dirt out of the mechanism, and your fan will start working again. Beats a hot night out in the woods somewhere, or a long wait for an appointment at the RV repair place.