Vent question

Hey y’all! I have a 78 c10 I’m working on. It’s an AC truck (at least it used to be, it’s all been disconnected). Anyways..now that it’s warming up outside I’ve noticed my blower motor stays constantly on. It stays on low and I get little to no adjustment. Every once in awhile I’ll be able to get it to blow high..but typically it’s just always on low. I also notice I don’t have any adjustment as far as vents bs defrost.

i initially thought it was just the switch at the the temperature control assembly, but I pulled the plug there and the blower still stayed on.

many advise on where to look now?Could my entire control assembly be wonky? And I’m not sure what’s considered normal as far as the blower staying on low or turning off completely (I know some newer cars the blower is always on). I’d appreciate any feedback..thanks!