I had who I consider a sharp HVAC fix my furnace a few years ago. Sticking fan relay on the control board. It's a 13 year old Rheem. Asked him about cleaning the evap coils, and he said they're not accessible without basically tearing it down. Told me not to worry about it, just change the filter when it looks dirty. Might not be a good analogy, but I've never cleaned an automotive evap and had good A/C on them for many years. I imagine they get leaf and twig parts stuck in there. Heard my squirrel cages chopping that stuff up sometimes. Every year I say I'm going to take the cover off the outside unit and clean the condenser coils. Maybe this year it'll happen.
--Vic