How to stop Xsara Picasso from misting up?

I own a Xsara Picasso LX. Earlier this year I changed some lamps on the heater control panel, to do this I had to remove the panel and the control rods at the back. Reconnecting was a nightmare but was finished. However two of the teeth on the hot/cold control snapped off so now I cannot get the heater to full heat, only about three quarters.
The problem now is , especially with the cold weather is the car gets steamed up very quickly. I have the heater on as high as i can get it and when the air control is on recirc, the heat is superb but as soon as I change from recirc to allowing air from outside the heated air goes cold. Is there anything I can do apart from the obvious which is to replace the heater control? I would appreciate any help you can give in this matter

Thankyou