A4 - Defrost in cold weather???

[Scott]

I have a 1998 A4 2.8Q.

I have been trying to figure out part of the climate control. Under normal 
conditions the compressor (snowflake icon) kicks on most of the time, and 
certainly if I hit defrost.
I have now been sub-freezing temps a couple of times where the windows 
start to fog like crazy. I switch to defrost, but the compressor does not 
kick on (I assume to prevent it icing over).

How the heck do you get this car to defog in cold weather?
In other cars I have had I could simply open the heat all the way & kick in 
the compressor and POOF, no more fog.

Thanks,
Scott