I had a prob with one A/C unit, dismantled all the plastic stuff and cleaned it, got my spirit level out to find the water run was not angled to the exit pipe, plus the rubber exit pipe connection was not straight it went up then down, there was a build up of cr-p in it because of that. Shoved a bit of plastic pipe in it and blew as hard as I could, I felt that clear a free passage, job done...