Warning: this will be a long post.
The other day, my wife told me that the heat blower was not working (we were around 0F degrees here last week). When I got home that night, I started the car, and everything was working so I thought she tried to use it in auto with the car cold (so no air was coming out). The following morning I started the car, and the problem was back. No blower motor movement at all, I tried to use it in manual and every combination of controls possible with no results. Then I got the ac flashing lights, so with 0F outside, I decided to take it to the dealer, but it was a saturday morning and we didn't have an appointment. They said that if I left it there they might look at it, but most likely it wouldn't happen until monday morning.
I called them up before they closed and they said that they would look at it on Monday, so after doing some research on the net I decided to take the car from the dealer and look at the blower myself.
I drove it home and started removing the pannel under the glove box. Then I saw a few drops of water on the inside of hte pannel. Once I saw the blower, I went to get the right tools to take it out, but before I did, I tried to use the heat again....and voila! it worked.
What happened was that the blower had frozen and leaving it at the dealer parking lot for a few hours (it was a cold but sunny saturday morning) and the engine compartment heat of the drive home was enough to unfreeze the blower (hence the few drops of water on the inside of hte pannel).
By the way, the dealer told me that blowers freeze often and they just apply heat to them and they work fine afterwards.

I believe what happened in my case is that we didn't drive the car for 2 or 3 days when it snowed 10 inches, and when I finally dusted off the snow, I probably pushed some of it down the vents by the windshield wipers. Then the snow melted inside and later on the water froze due to the low temps.
However, as explained above, once all the water dripped out of the system...everything was fine.
By the way the dealer told me that they had many cases of frozen blowers that would work fine after applying heat to them.

94 850 turbo 56kmiles