It sounds like your condensate drain is plugged and the drain pan is overflowing.
You can try sucking the condensate drain tube out with a wet-vac. If that doesn't work you can try blowing compressed air into the drain to dislodge and muck and then suck it out. If your condensate line was installed properly there will be a removable cap near the P-trap to aid in cleaning.
"The physician can bury his mistakes, but the architect can only advise his clients to plant vines." -- Frank Lloyd Wright