Yep It's condensation, The alternatives are, Plug the drain,(this should be easy it happens to alot of volvo's) the result will be "about a liter of water" on the passenger side floor board, Be advised this is very hard on carpet and will affect interior air quality adversly...(insert your own nasty smell)... and will cause the floorboards to rust very quickly...Then the water will drain out leaving a puddle on the garage floor.
The only other soulution is to not run the a/c.
sorry bout the sarcasim. but I have just been contemplating the fact that I'm going to have to go completely through my a/c before hot weather...$$$, yours is working fine,
Stay cool
Bret
--
rust free in west Texas