00 GMC Sierrq heater issue

[edgein72]

I have what is probably a silly question. My heater blows hot air but the selector doesn't work so it only aims at the floor. Also the AC doesn't work. Could it be as simple as replacing the dash unit (pictured here). I'm a tad short on funds so I don't want to take it to a shop. I have a 99 Tahoe in the driveway that I was going to check to see if the units are the same because the heat worked perfectly in there. What else might I look for to get the direction selector to work ?