Fog machine instead of heating

Hey, guys,

I hope you can help me.
I changed the coals yesterday at my alternator, after that I wanted a round ride to see if it was going right again...
At first I drove without heating, but then started to start the windows, so I turned on the heating, but instead of making the windows free it got even worse.

Steam flowed out of the vents. It was from the cooler fluid.
Then had to drive, because within a short time the whole car was full. Despite open windows. I then switched off the heater again, but it still came out steam. I drove home the few meters, then I saw at home after the water, and there the balance tank was only half full.

Now my guess: can it be that the heat exchanger is leaking, and the cooler water has thus entered the ventilation ducts?
And where is the heat exchanger? Still got the old climate. (PT bj. 89)

Ask for help.
Ms Alex