The blower fan in my 2008 Subaru Outback starts freezing up when it's about 0 degrees outside. After I drive it for 10 or 15 minutes, the blower comes on and works very well.
Until it comes on, I can't defrost the windshield and it's pretty darn cold.
I'm not sure if it's really frozen or what the actual problem is.
Note, I live in Fairbanks, Alaska, so we'll be seeing temps like this for the next several months.