Why is my AC leaking water inside the car?

Water on the passenger-side carpet with AC use is a plugged evaporator drain. The evaporator condenses cabin humidity out of the air — normally that water drips out a rubber tube onto the pavement under the car. When leaves and dust plug the tube, the drain pan overflows into the cabin. The fix is usually free: find the drain hose (under the passenger footwell), pop it loose, and blow through it with compressed air or a wire. If it's coolant instead of water (sweet smell, greenish tint), that's a leaking heater core — a much bigger job.

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