I tried to do a search for this but got information overload.
My 2002 explorer is stuck on defrost. It doesn't matter where the dial is.
Recently, I found some acorns in the blower and got them out, but since then
it's stuck on defrost. What did I screw up?????

 

Defrost is the "default" setting, if vacuum is lost it will automatically go to the defrost setting to be sure the driver will be able to clear the windows.

I'd check and make sure you didn't knock the vacuum supply line off.

 

I'm with danr1; you have accidentally knocked the vacuum supply line off when you removed the acorns. Simple to fix.......find the line and replace it back on the nipple.

 

Thanks for the replies.
Seems like Mr. Gumby pinched the vacuum line.
All fixed.