I have some ivy & wildflowers growing near mine that help, but not 100% camo.

what about a containerized plant, or conifer?

I hid mine a few years ago with a piece of white wooden fencing. I attached an "isolated" bed (large narrow window box) at the bottom, sunk the box in the ground, and used it for a small annuals bed.... the fence hid the unit and morning glory hid most of the fence. :)

What's your budget?
I found an old wine case, removed the top shelves, installed a yardsale armillary on the top remaining shelf, and planted shade tolerant clematis and goldflame honeysuckleon on the outsideof it. Then, to the side, at an angle, added two flat trellises, with goldflame honeysuckle between them. Underneath, I set 'Rozanne' perennial geraniums, spring blooming bulbs, columbines, and geranium macrorhizum, 'Biokova', 'waterfall' campanula, mukdenia, and isotoma.

How deeply shaded is it? No matter what the site limitations are, you still have a large number of options.

I have almost the exact same problem here... Mine is under a mature hemlock that I've limbed up a little and I've tried many different things, but so far I've had good luck with a clumping bamboo of all things... Fargesia nitida has done very well in the shade, though I do supplement water during the summer... Also I have to second the Ivy thing.. It too has done very well growing up a trellis on the opposite side of the A/C...

Our last house had 3 or 4 burning bushes planted around the a/c unit, out about 2ft and it hid it great! I'm sure they were there awhile, it may take some time to grow in, but it worked.

Kerria japonica 'Pleniflora' will bloom in full shade....just a thought.