No direct help as I'm lacking experience with AC or workhorse. But there are some really good intense online info which I can pass along as a place to start.
Don't skip over the line on how to decode the VIN as that can give lots of exact info on other points like the engine that you will likely need to sort the info.
From past looking at the blowers, I think of it as being a set of resisters that control the fan speed, so you may be looking at two different question?
Approach that with care as it is a really foggy memory!