96 Grand Cherokee Water on Passenger Side

1996 Grand Cherokee A/C Every once in a while the front passenger side gets flooded with water from beneath the dash. I think the A/C evaporator pan overflows. Sometimes the A/C does not blow even cool air. Could this be because ice has formed on the evaporator? How can the drain tube be cleaned? Where is it on the outside/underside? How can I keep it from clogging? Thanks.