a building science article that in part addresses what is going on is Chad's house.
only part of the article...see picture #4
http://www.buildingscience.com/docum...rces/retrofits
Photograph 4: Window Condensation - Interior moisture levels go up due to reduced air change and relative humidity adjacent cold window surfaces rises sufficiently to condense water. How to fix this problem? Lower the moisture content of the interior air with dilution ventilation or warm up the surface of the windows by replacing the windows with better windows or do both.
So Far:
1-reduced Rh by adding dehumidifier
2-are the kitchen vent fan & bath fans vented out of the attic?
3-leaving fan set in on position..in case there is condensation in the duct work. as per Teddy Bear's postings.
4-windows...see my first post about metal frames of windows & condensation.
also...while letting the blower run in winter to resolve the issue of moisture in ductwork that is potentially ongoing,
the side note to that is fan setting in the summer.
for cooling season when a/c use is constant, you set the fan to auto.
reason for that is...RH removed by a/c will collect on coil, when fan is set
to on position...it releases this moisture back into the house when compressor cycle ends.
when fan shuts down as unit shuts down, the moisture then is released to the pan
and drains away.
so...are your kitchen & bath fans vented out of the attic??
best of luck.