2002 t800 blower!!

It wont affect your blower, it eliminates a bad design loop on cycling the compressor though.

But if your blower is always going but sometimes you have to turn off the ac and after 10 minutes it blows better, your cores in the blower box may be icing up and restricting airflow, in THAT case it would help by cycling the compressor off before the core freezes and blocks airflow

 

This is likely a loose electrical conection if its fine while sitting but while driving the blower stops or is intermittent

 

Double check your switch replacement splice job, turn truck key on and switch on, then wiggle those wires, if that doesnt work, same operation, but open blower cabinet and wiggle the blower connection wires, hopefully its just the spade connections not being seated right

 

Blend doors are air actuators. Defrost i beleive is all of them closed, When you hit the others, do you hear any clunking? Or just tiny clicks? (Or nothing?) If nothing at all, you may not even have air supplied to the unit. Though from my understanding, this should only affect which vent things come out of, the top slider tells the air switch where to be, it also tells ac compressor to kick on at ac, defrost (ends) and the very center one. There are no ac electrical contacts at vent and heat (in a line starting at ac all the way left positions those would be 2,4)

But the blower switch is its own thing too...