I turn on the air conditioner and it blows cold and the fan works fine. Then I hear the fan belt slip a little, a slight squeal, and all of a sudden the air now is blowing out of the defroster. In a minute or so it reverts back on its own and works fine again.

 

It's too bad NOBODY can help you when you can't tell what in he[[ you have for a vehicle. Chevy, Yugo, or Toyota ????????????????

 

Sounds a Like issue with the diverter. This it usually a vacuum power flipper door to change the air output from vent, defrost or floor. They are sometimes all electrical or a mix vacuum and electrically controlled.

Please post your model and year and some kind person with an electrical/vaccum diagram may just post one here.

 

Sorry, I have a 95 150 4x4. auto trans