[carpdad]

Your siding should be chalking, which is a fine powder of paint will be washing off with a gentle brushing. Power washing alone may not be good enough. You may have to also scrub off the old finish and rinse off.
Then wait at least 2 weeks for water that WILL have got under the joints. Then wait further for at least 3-4 days of sunny weather. You can use the power sprayer but also back brush. Leave a thin layer between vertical and horizontal joints. Don't paint on the sunny side. 1 primer then 2 coats finish.

 

[carpdad]

You can rent power sprayer, but the advice on over spray and wind is important, esp around the garage and cars.:smile: BTW, learning curve on using the sprayer is fairly short. Keep the coat thin and do 2 coats. I am reminded and agree that a primer may not be needed. Research this further.