A/c is on and passenger front floor boared is flooded

If this happens after you've run your AC and it's water, then you have a clogged condensate drain. The condensation can't drain out and fills the heater box until it overflows. See this post on clogged drains.
https://ricksfreeautorepairadvice.com/passenger-side-carpet-wet/

If it is equipped with an air conditioner,probable cause would be the a/c cooling coil drain pipe may have come loose or clogged, thus making the condensed water from the cooling coil to spill over on the carpet. Have a look under the box that holds the cooling coil, there should be a drain pipe that goes through the floor towards the front.

if it's just water, check the door gaskets. if it's coolant, you'll most likely need a heater core. past that, have someone spray water on the car while you look for where the water is getting in. you may need to pull the carpet back some to see.

The a/c drains the condensation water out thru the floor by a small hose or tube.
If you look under the van near the passenger side floor at the firewall you should see a small tube and it may be stopped up.
You may have to put the van on a lift to find the tube.

You could have a windshield that is leaking water. Often this water will trickle down from the bottom/inside of the glass and then down the firewall, under the carpet or floor mat, and to the floor. The way I usually hunt for these is to remove the floor mat or carpet then get a flashlight and lay down in the cab so you can see under the dash area while someone sprays water on the vehicle with a garden hose. Often the leak will show up as a trickle that you can then backtrack to it's source. Another spot to look for is at the cowl in front of the windshield where air for the heater and a/c is pulled into the passenger compartment. The water drain holes in this area can plug up and allow water to overflow into the passenger compartment. Good luck, hope this helps!

Your AC overflow is clogged up, it needs to be cleaned out. It is a little rubber hose sticking through the fire wall on the passenger side up front, bugs and dirt get in there and clog it up, then the ac will flood the floor. The seat can be unbolted from the floor and lifted out, these bolts are fine thread and high torque, meaning it takes a while to get them out, if you have an air ratchet , use it. The chair is probably wired down, so don't forget that when you have an arm full of chair and can't move. Hope this helps.

I would say you have either a bad seal on the windshield or the seal on the passenger door opening.

I think that I can help you. It sounds like your drain-tube is plugged up. Get in the passenger side, and pull the carpet back from under the glove box. Look for a black rubber pipe that goes from a black box, and pokes thru the firewall, on the passenger side. Remove the hose from the box, and have a container ready to catch water. If water comes out of the black box, your drain hose is plugged up. Clean out the clog, and you will be golden.

Your air conditioner water drain holes are blocked. Check the exit holes for water from the evaporator unit under the foot wells or dash unit. Through these holesor unblock these and the water will flow through to the outside

Yes I know, but If you hold the accelerator pedal to the floor on a fuel injected car, the Throttle position sensor will tell the computer to enter clear flood mode. Then the computer will shut off the fuel injectors while you have the pedal to the floor. If it is flooded, you should be able to get it started in clear flood.