Wasp nest in a/c unit, how would you deal with it?

Sevin powder. Dust it liberally in and around the entrance to the nest--a plastic ketchup bottle works well--and the wasps will be dead in a couple of days. The advantage is that, unlike the sprays, it does not enrage the wasps, they just go on about their business, tracking the Sevin in to the nest where it kills them all.