Durango defrost problem

We are having a problem with our 98 durango. The heating system blows out a small amount of fog all the time (turned on or off) and when the defrost is turned on it does a very poor job of clearing the windows. It seems worst when it is raining. Also the air conditioning stopped working last fall, we recharged it twice but it would quit again with in a few days. I don't know if this is related or not. Any help would be greatly appreciated!