Our 2006 Monterey 39' w/2 roof AC's ........ read in the operators manual that the only filters to clean are on the inside intake drop down door. All there is  .... is a piece of 1/4" foam that covers the inside of the grate. Didn't read of any external ...... are there some on the roof? Seems too simple. Reason I ask is .... we are parked near a sheding Cottonwood tree with the AC running (it's 94 degrees today). Are we sucking  cotton ????????

Roof A/C units are designed to recirculate air inside the coach, and therefore there is no need for an external filter. The filter that you found should be the only one, but if there is a lot of "cotton" in the air you might need to clean the condensor coil fins on the roof.

Gerald

My oldest son is an AC technician and reccomends cleaning the condenser annually for maximum efficency.  He uses a special cleaner but water or a vacuum is OK and does not have any effect on seals.

As long as we are talking rooftop A/C, I found great A/C filters on Ebay. They are 3 piece mesh, fiberglass & charcoal filter. You trim them yourself and they are much better than the foam filter. I did not have room for the charcoal filter and did not use that part. They would be good for people with allergies. Did not have any problem with air flow.

Just look for RV A/C filters.

Mike

Excellent input everyone. Much appreciated .... The best resolve of a problem is the visibility of a solution.