Cleaning my HVAC system

I have decided that it is time to do a thorough cleaning of my house, and I am starting at the top and moving to the bottom.  I have thoroughly cleaned all of the floors, and I have scrubbed all of the furniture.  I am also working on the walls, and scrubbing all of the fixtures, along with cleaning all of the ceiling fans and lights.  I plan on leaving the HVAC system for last.  This seems like the right thing to do since I am working my way down from the attic, to the basement.  I’m really not looking forward to cleaning the HVAC system.  I don’t know a lot about a heating and air conditioning system.  I have no idea where to start when I clean it.  I know that I have to take out the old air filters and replace them with new air filters.  I also know how to stick the vacuum hose inside and clean the dust and dirt from the unit.  I have read that there something called a condensate drain in my air conditioning, and that it can have algae grow in there.  I know I want to get rid of the algae, but I don’t know what the condensate drain looks like, or where to find it.  I also heard that mold can grow on the cooling coils, and there is another problem.  Where are the cooling coils and how to access them.  I don’t know if I am going to be able to do the HVAC system, but I think I’ll give it a try.