Hi Val
I find just spraying is not good enough. If you also use a bottle brush or an old tooth brush to brush the blades along with the cleaner then I can get them really clean. Then if you have oil holes (Usually on the room blower or older non sealed exhaust blowers) a couple drops of 3 in 1 oil are needed.
I also use a putty knife to scrape behind the blades of the exhaust blower, and then when they are all clean, I use Spray Graphite from the auto parts store to give them a nice coating. In my experience this spray graphite really helps keep the build up way down so you can go longer between cleanings!
See my pics here. (Note: These pics are for Mature experienced Stove users and may be explicit and not very interesting to non users!) LOL, LOL
Wood Pellet Stove Yearly Cleaning - Convection Blower
https://www.hearth.com/talk/threads/60351/
Wood Pellet Stove Yearly Cleaning - Exhaust Blower
https://www.hearth.com/talk/threads/60251/