1991 Honda Civic 1991 Honda Civic Coolant Leak

Your heater core could be leaking, just look under the glove box and you will see a big black heater housing there, if you see coolant leaking from there, your heater core is leaking.

Do you have a diagram of what it looks like?

I was unable to upload a diagram, but it involve in removing the dashboard and lots of other components to replace the heater core. You should try radiator stop leak to see if that will stop the leak.

Did you confirm it is coolant or just water that is causing the carpet to be wet? Coolant leakage into cabin would have the radiator running dry, make sure you check the level.

Coolant would be from the heater core as answered by kng1818 but if it is just water, it could be the the AC evaporator (cooling coil) housing drain hose has been dislodged or clogged .

You would have to remove the dash to get at the heater core.

This is the heater unit under the dash.