Not a whole lot to go on, but a standard thing to check whenever you have this problem is to see if the little drain tube, normally under the bottom of the dash, that leads out the car, normally either through floor or firewall, has been disconnected at either end. The tube carries the water that condenses from the a/c unit or climate control, keeping in mind that using the heater/defroster can also remove humidity from the air. Another reason for water leaking into the passenger floorboard is a bad heater core.
Passenger side of the firewall.
sounds like you need to replace the heater core
under the passenger seat
Front passenger side of the engine.
If equipped, it is on the passenger side front of the engine.
I have a 1978 Sierra 1500 and mine is near the secondary tank, passenger side of the truck.
Not a whole lot to go on, but a standard thing to check whenever you have this problem is to see if the little drain tube, normally under the bottom of the dash, that leads out the car, normally either through floor or firewall, has been disconnected at either end. The tube carries the water that condenses from the a/c unit or climate control, keeping in mind that using the heater/defroster can also remove humidity from the air. Another reason for water leaking into the passenger floorboard is a bad heater core.
This is from the seal around the vent on the outside portion of the panel. Check the seal and use some silicon to fix it up.
all passengers
Bad heater core? replace Evaporator drain plugged if A/C equipped - try to unplug from under vehicle
If its a 96 you need to unbolt the center seat, Then there should be four bolts on the floor.
in the heater box behind the dash on the passenger side of the truck you have to remove the dash to get to it