Why does water leak into the cab from the air conditioner?

The condensate drain at the bottom of the plenum is blocked. It can become blocked from different causes but the fix is the same in most cases. Stick a wire up the drain tube to clear it. You'll probably need to put your car on a lift to see where the drain is.

Some AC installations have a drain tube or tubes that connect to the drain at the bottom of the condenser and carry the condensate water through the floor pan. You will find this on older vehicles with condenser units slung under the dash. The tubes can become kinked or fall off the unit.

One way to troubleshoot this problem is (hey, the floor is already wet) to pour water through a dash vent and see where it runs out. If the water leaks out a joint, you probably have a clogged drain. If it leaks through a crack in the plenum you'll need to dry everything out and patch the crack with JBWeld or a similar product.

After you locate the leak, take out the carpets and padding and dry it all so your floor pans don't start rusting.