I found water in the basement, around the furnace. The air conditioner has been running for about 6 hours -- it is HOT outside too (about 90 degrees). Any suggestions as to why this happened and what can be done to remedy the problem?

Likely the condensate drain plugged up and the condensate ran over. There will be a cabinet next to the furnace that the lines from outside go to. There should also be a small line coming out the bottom and going to a drain or something. The lines tend to be small and have generous amounts of sharp elbows, plugging easily. Open the cabinet and try poking a wire in it. You can also blow air in it.

Thank you so much.

My husband came home, looked at everything and saw that the line which drains the condensation (which runs into the set-tub in the laundry room -- 25 feet away) was plugged. He cleared that which seemed to get the water moving a bit. He also plugged the 'pump' in and it didn't seem to do anything -- are they particularly quiet? Would we hear something when that pump is plugged in?

The pump could have a float switch that only turns it on when there is water. The float switch could stick too.