froster not defroster?

[RODNEY MICHAELSON <HOTROD@pacbell.net>]

Can one of you help with a problem with my daughters '91 90?
Here in the Northern California where the rain has come to live
day in and day out my daughters '91 90 when she turns on the defroster
(it has automatic climate control) the front windshild will fog up 
instantly and take a few minutes to clear up. I first noticed it back in 
September when I was on the freeway and hit the defrost button. BAM, the 
world vanished in a mist. It would happen every once in awhile after that 
but now it is everytime according to my 16 year old daughter.
Any suggestions?
My '86 5kcst with the same climate controller has no problem and my 
wife's '95 90q doesn't either.
Thanks for any help or ideas.
Rod Michaelson
Walnut Creek, CA