Exhaust duct from microwave fan

never have cleaned any of my microwave ducts...I've had 3 5th wheels.

I haven't cleaned any ducts.

My micro vented back into camper by a fan in back to the front grill.

john&bet wrote:
My micro vented back into camper by a fan in back to the front grill.

Wish I could say the same. I know they make ductless fans but ours is vented. I have never taken off the vent cap to look down there but the roof is just black around and only that area. We have filters an the face of the fan and they're clean. That's what makes me scratch my head regarding the dirt on the roof. :h

Whenever there is cooking there is grease! It matters not how little eventually some of it will get sucked through the vent and some of that will deposit itself around the opening. Dirt will naturally accumulate wherever that grease lands.