highly likely heater matrix, or could be a split pipe. Basically engine coolant circulates through it, and the blowers blow air through it, thus providing warm air for the car when you put the blowers to hot.

For a quick fix, look behind the engine, you will see two pipes coming from the back of the engine, through the bulkhead and into the car. Remove one of these pipes from the matrix, and connect it to the other hose, thus disconnecting the matrix. Heaters won't work, but will prevent scalding hot water pissing all over ones feet!