heater fan speed control inop for 5 minutes??

[JStieger]

I just went through 17 pages through a TDR search and can't seem to find a clue to the following:

-Had truck block heater plugged in all night and through this morning.
-After starting the truck at 4:00 am when it was about 0 degrees I was expecting to get some luke warm air out of the heater vents. What I got was nothing blowing - no cold air, no hot air, nada...no heater fan noise whatsoever on any fan speed or HVAC vent position.
-I was thinking that a fuse may have blown so I went to scrape the windows. I also left the heater fan control speed on medium anyway. After doing the windows for about 5 minutes I get back into the cab and the heater fan decides to start by itself!
-Played around with the heater controls and speed and everything ran fine as if nothing ever happened.
-After work in the parking lot it was 15 degrees and the truck started up with no heater fan speed issues at all

When I got back home I searched on the TDR and found the TSB 24-004-03 for the broken defrost door, but it doesn't seem to apply to me because everyone else seemed to have heat and the blower speed albeit not in the right place.

Any thoughts?

The last time I drove the truck was a few days previous. It was snowing, but the air was pretty humid yet hovered around freezing. The days since then have been a "dry cold". Could it be that maybe the AC or blower "froze up" temporarily due to the sudden change in humidity coupled with running the AC that runs on most of the heater settings?