fogging windows on 9500

It sounds like you have a leak in your heater core, same symptoms anyway. When it fogs up is it like a slippery film on the windows?

have you checked the air conditioning drip pipe is not blocked up with crap, usually the pipe is behind the left front wheel, had this happened to me on a 9610, ended up with water under the mat in the cab and was like a sauna,until we worked out what it was. if it is this you will have to pull the buddy seat and blow the hose out with an air line.

Check your cab filter on the outside of the cab, if its plugged it will absorb moisture and that can cause it. There is also a filter behind the "buddy" seat in the cab. to access it you have to pop out that tray above the budy seat and reach down in there and theyll be a filter with a handle. when our 9500 fogs up like that i know its usually time to clean the filters.
Hope that helps.

are you giving it time to warm the window up when you have the defroster on.

i would check to see if your air conditioner needs a charge. if it is not working it will affect the defroster. even when it is cold outside the a/c is used to dehumidify the air before it is heated.

I have had that problem on a 60 series combine around 10-11pm at night and you have to have the slightest bit of AC on to keep them clear. Not uncomfortably cold but just enough that if your get over eager with the heat you get fogged up. Never did find a problem with the combine there was just alot of humidity in the air one season.