Tales from the '05 GMC Canyon: Blown Resistor
Yesterday I went to turn the air conditioning on in my truck and the first three (out of four) settings didn't work. Only the highest fan speed did.
I had a very similar problem on a 2000 Oldsmobile Alero. Turned out to be a blown resistor.
It seems the exact same issue is happening with my truck.
Today I will be taking the truck in for service. If all goes well, this will be under $100 total including labor. At the most $150.. hopefully. It depends if the entire board needs to be replaced (which would very very costly) or if just a small portion of the board needs replacement.
The truck has around 55,000 miles on it at present.