I too am in NY, zone 6b, and am disappointed in the several clethras I have. They are so late to leaf out that I almost took them for dead in June, and again in late summer when they probably went into early dormancy because of the drought, even though they are planted in what I consider a damp area with partial shade. The ones I planted in the shade of maples succumbed quickly. I have quite a few viburnums that do well once established. However three viburnum dentatum (arrowwood) I planted were immediately decimated by deer. I am protecting what's left of them in cages. I have learned that just about any new plant needs initial protection. Deer have never touched the ilex or boxwood and they are evergreen. Mine do fine in partial shade. They grow awfully slowly and don't achieve the height I would think you'd need for a screen. From my experience, the best deciduous shrub for your needs would be forsythia because it is tall and dense, so that the bare branches are still a screen. Even better would be an evergreen viburnum. I'm sorry I don't know the name of the ones I have.

Thank you! I've scratched clethra from my list! Are the ilex you have ilex glabra?

While Clethra probably doesn't make a good screen, I like it as a shrub in the right area. I have it in a mixed shrub border and along the edge of a wetland area. Right now it's a beautiful clear yellow. I have 'Ruby Spice' and it's quite slow growing in its current settings, which have poor sandy soil underlain by clay that keeps it moist. From cuttings after about 10 years it's 3'-4' tall in full sun.

You may get more ideas as far as solutions to your problem if you post photos of the area taken from the most common viewing points. I don't currently have a feel for the size or shape or type of shade of the area. Are there overhanging trees or closely adjacent buildings that make it really dense shade? Or is it relatively open other than the house to the south of the area, creating a brighter shade with reflected light in the area you want to plant?

I honestly think that you should consider a non-growing screen with plants in front of it. That will block the sight of the air conditioner, and you can plant a combination of shrubs and flowering shade perennials in front of it to distract from the lattice or fence without having to worry about density and height. It will give you more flexibility as far as what you plant since there aren't many shrubs that will both grow densely in shade and be resistant to deer. Here is a thread from the GW Perennials Forum that shows the type of thing I am suggesting, though the screen itself could be denser that WoodyOak's current one.

Sometimes having something nice to look at close up is enough to distract from the problem area, and layering is often more effective than a single row of plants. For instance, would a small tree close to the raised deck give enough screening from that vantage point?

IME Ilex glabra doesn't grow particularly densely, but might be OK in combination with a fence-type screen. I don't know how deer resistant they are, however, since my deer prefer to stay away from where people are. The more common prickly leafed evergreen Ilex are eaten by deer IME. Toxic plants such as the tall shade-tolerant perennials monkshood/Aconitum and foxglove/Digitalis will be left alone by deer due to the toxicity.

a pic might get you better brainstorming ... ken

Great idea! I posted pics on a new thread. Thanks so much for any ideas!

florava - it's a good idea to post pictures but could you post them in this thread too? Two threads can soon get separated on the forum and people won't necessarily see them both. Then you start getting answers at cross purposes and confusion reigns.

Need pics here. I actually like the ilex glabra idea.

Sorry for the confusion, posting pics here. Someone else recommended snowball viburnum, which I happen to really like, so that's an option too. The grey gravel will be grass or a bed, depending. You can see the deck (where we spend a lot of time and is the reason I want to plant out this area) and there is a railing on the other side of the stairs and by that railing I was thinking of planting twist and shout hydrangea, an endless summer. The machinery is two feet from the garage, no idea why, but it makes it a slightly awkward layout for planting. We never use that garage door but I do think we need an open space there. Thanks again, everyone.

No Viburnum. I would think columnar plants would be best, something that could be chopped down to a certain height if the AC needs work. You could coppice forsythia or go with one of these suggestions:

Buxus sempervirens 'Graham Blandy'

Platycladus orientalis 'Morgan'