I have a 97 Pontiac Grand Prix which has an apparent water leak when it rains; the front passanger floor is wet. I have pretty much determined it is not from the door seals. What would be other sources of this leak? How do I rule out other possibilites?
If the ventilation system drain tube is clogged, rain water can spill into the interior through the heat vents. The drain tube is on the firewall, low on the passenger side of the car.
Are you sure the water comes through the heating vents rather than dribbling in from somewhere behind? (Why else to check door seals?) I’m thinking maybe you have a faulty windshield seal.
You will need to pull back your passenger side carpet and have someone on the outside use a garden hose and spray water all around the windsheild and door and door glass while someone on the inside looks for any water coming in. I’ve used this method several times to find water leaks.