Might be some sort of insect or slugs. I know slugs typically cause obvious leaf damage which doesn't look anything like wilting (which you said your plants were doing). But I had similar damage to some of my ajuga and when I investigated I found loads of slugs and pill bugs. The ajuga was planted between concrete edging blocks which line one of my beds and that area in between the blocks stays kinda damp....perfect environment for slugs. Damp, cool, and dark. Might wanna dig around the base of your plants or go out at night with a flashlight to see if you can spot any slugs hanging out in the area where your ajuga is planted.
If you don't see any bugs/slugs, pull up one of the plants and have a look at the roots...the excess moisture from the dripping A/C might be causing root rot.

Renee

Thanks Renee - Do you know, if the problem is slugs (and I have seen a couple here and there) or pill bugs (I don't know what they look like) - is there a solution for that, other than removing the ones you see? Anyway, thanks for your input.

Pill bug/sow bug/roly-poly....little bugs that roll themselves up into a ball whenever they're disturbed. They normally only eat decaying plant tissue, but have been known to munch on the fresh stuff if they're hungry enough. If you find them amongst your ajuga, it may just mean they're eating old dying foliage that has already been damaged by something else....not necessarily the perps of the damage you're seeing on your plants. Pill bugs live in and around dark moist places.

As far as the slugs go....diatomaceous earth (DE) or crushed egg shells work well. Just sprinkle the stuff around the base of the plants. The DE will have to be re-applied if it gets wet, though. Remove any rocks, boards, or other objects snails/slugs can hide under....removing their daytime sheltering spots helps out quite a bit.

Now, this is all assuming your problem is being caused by slugs.....could end up being something else entirely.

Good Luck,
Renee

Here is a link that might be useful: Pill Bugs