If you plan on cleaning the coils on a continual basis,start to convert the plenums to increase your time. If you can get to the backside of the triangle plates on the A coil it is easier access than going thru the distribution network in the front. Cut a rectangular plate out of the plenum and make up a door you can take off easily. remove the access steel from the coil and lay a pleated filter over the heat exchanger to catch any loose debris that falls. vacumn first with a soft bristle brush and then spray your cleaner on and flush off with a spray bottle of clear water. any residue will go down into the drain pan. run the fan only on the furnace when your done to dry anything you got too wet.