Why does water drip into your car when the air conditioner is on?

SUGGESTION: CHECK FOR A PLUGGED "CONDENSATE DRAIN TUBE" SOMEWHERE UNDER THE HOOD; PROBABLY CLOSE TO THE HEATER OR AIR CONDITIONER - YOU HAVE PROBABLY NOTICED CARS ON A HOT DAY DRIPPING WATER UNDER WITH THE A/C RUNNING. THIS IS THE WATER THAT IS DRAINING INSIDE YOUR CAR INSTEAD OF RUNNING OUT THE DRAIN TUBE TO THE GROUND. IF YOU LIVE OR PARK IN AN AREA WHERE THERE ARE SMALL TREE LEAVES OR SEEDS DROPPING, THEY CAN ENTER THE HEATER/AIR CONDITIONER'S FRESH AIR INTAKE AND SETTLE ON THE BOTTOM OF THE PLENUM, EVENTUALLY COVERING THE HOLE LEADING TO THE OUTSIDE DRAIN. SAME AS A PLUGGED DOWNPIPE ON HOUSE ROOF GUTTERS. HINT TO FIND THE DRAIN TUBE - TURN ON THE HEATER/AIR FAN WITHOUT ENGINE RUNNING (SO YOU CAN HEAR IT). WITH IT RUNNING, LISTEN UNDER THE HOOD FOR ITS SOUND. THE DRAIN TUBE YOU ARE SEEKING WILL BE SOMEWHERE NEAR AND BELOW THIS AREA; THERE IS A CHANCE YOU CAN CLEAR THE OBSTRUCTION BY BLOWING BACKWARD THRU THE OPEN END OF THE TUBE. CANNOT GUESS WHAT'S ON YOUR CAR BUT USUALLY THESE TUBES ARE APPROXIMATELY 3/4" DIAMETER, 2 - 6" LONG POINTING STRAIGHT DOWN.