1999 Buick LeSabre has no cabin filter but leaks water onto passenger floorboard. Any suggestions?

You need to find the drain pan line that comes through the firewall. Open the hood and search for the line on the passenger side firewall. The line is probably clogged from insects, animals, or other gunk. use a short piece of dowel or wire to unclog the line and allow the pan to drain to the outside of the vehicle.

is your passenger side floor board wet? is so its your heater core. if not i have no clue what to tell you

there are none. you either have a bad heater core or your air conditioner drain hose is clogged. It should be draining above the shock on the passenger front side.

If it is just water start with the AC, if it has coolant in it then its the heater core.

Sounds like the A/C condensation drain is plugged. I hope this helps!

I had a cadillac that this happened in. It's the passenger cabin air filter under the hood. U need to find it, open it and get all of the leaves, etc out of there. It's kinda nastly but at the bottom there should be a drain to get the water out of. This solved the problem for me. Hope it helps!

I would try to determine if you can put some expanding foam in the crack in question where it is leaking.

Look for moisture on the glass of the windshield, as well as the passenger side door, if thebottom seal isnt making contact on the door glass water will run in threw the door

Remove the cowling that covers the vents below the windshield. This is where the cabin air filter is located. Should have two popup buttons and a screw button in the middle. Once cowling is removed, you will probably see a 2' long rubber gasket that has come loose and is probably hanging. Apply some silicone to the groove in the gasket and replace. Water is running down the windshield and into the cabin air filter area and down onto your floorboard. This is a good time to replace the filter while you have it off. Hope this helps.

Having just repaired this problem in a 1998 Buick Regal, I can tell you that fixing the water leak is actually quite easy. It took me quite a while to track down the source of water, but I have discovered that it comes through the cabin air filter. There is a seal on the passenger side of the cowl (A two piece unit, black plastic, against the windshield) that seals it to the windshield to prevent water infiltration. It is very small and somewhat hard to miss. I took the cowl off to change the filter when I discovered this.

You can make a diverter to go over the air filter under the cowl, or even easier is to use some clear RTV silicone (avalible at any automotive and most hardware stores) and put a good bead on the old seal. When you re-install the plastic cowl, be carefull where it goes against the windshield to make sure you don't "smear" the silicone. After you re-install the plastic retainer hardware, smooth out the bead and clean up the excess silicone(a wet finger and some old cardboard works great). Let it dry and clean up the water in the passenger compartment.

Cleaning up the water is the hard part. Removing the plastic trim around the door (if you grasp the trip peices firmly they just pull up off some metal clips,but they can be quite stubborn) you will notice the carpet just pulls up. At the bottom front corner of the front doors the carpet has a plastic hook that is around one of the trim clips. Lift it off that and the rest of the carpet towards the firewall just pulls up. If it has been a long problem, your carpet may be moldy. Also, the carpet edges and some of the more hidden panel clips are very sharp and may cut you while you are poking around, so be carefull.

Since the water entered through the air filter and right over the fan, you will at minimum want to replace the filter. I had mold and moss growing on mine. My fan also squeels and chirps now, so I know it got wet. Not much to do about that but replace it or carefully lubricate the motor.

In your question you mentioned a door underneath the filter not closing. On my '98 Buick Regal there is no door or valve of any sort. The filter sits right above the fan blades. It is the cowel's job to prevent water from entering this part of the vehicle. I hope this helps you fix your problem.

Here is what all dealers do to find water leaks, we spray a fine mist of water on the car near where the water might be comming in with a spray nozzle, someone gets inside the car and look for the leak, there is no other way, and I have been doing this 30 years.