Major amount if water filling both floorboards, drivers and passengers

Found water flowing from firewall behind brake pedal. My friend removed the hose going to the heater core and bypassed it. Wow, what a difference in inside temp. Much cooler now that hot water isn't spewing into my car. Heater core seems intact. Only because I have not smelled antifreeze nor has it blown up on my windshield. At first I thought the ac condensation was draining into my car. I cleaned out the ac drain line, thinking it was clogged. Any suggestions before I take out entire dash and replace heater core un-necessarily. Also if I do have to pull dash, I want to fix my lever that changes my vents, from, ac, to heat, to vent, to defroster. I've heard there is a little barrel shaped part with like a little finger on it that makes the temp change to ac, or heat, etc. No one seems to know what that part is called