heater question and a dumb one

[TxRat]

OK here's deal. This is the first early truck I have owned so I'm still learning.

My truck is a factory A/C truck that has two sets of controls. One is for A/C and the other is for heater.



I have these controls



The middle knob turns the blower motor on by pushing it down correct?

the left knob directs hot air to the defroster by pushing it down?

the right knob directs hot air into the cabin by pushing it down?

My fan doesn't come on but I also can't get the middle knob to move. It appears to be jammed. I just need to understand how it works before I tried to fix it. Has anyone else had the center knob jam up and what can I look at to repair it...