When I bought my Mustang and it had 2 pipes of pipe cut off that I believe run from the radiator to the AC/Heater. I'm guessing it was because of the same problem, it must have been leaking like your car, because the Heater doesn't work now, it just blows cold air. I still haven't fixed it.
They're the two hoses shown in this pic, it's not the same car, but they're in the same location.
Can anyone verify what those hoses are for?