Camco screens for hot water heater and furnace. Find them at any camping store and even at walmart.


Why they don't put these on at the factory is beyond me.
For the fridge unit I just bought the same type screening from a hardware store and cut it to fit and taped it on the inside of the louvered vent cover.
Your air cond roof top unit should have a factory screen cover on the back of it. Check to see. I have seen them pulled off by going under tree branches and the owner doesn't even know it. Looked at a lot of used units where it was gone.