2012 t660 can't turn heat down in cab, any suggestions?

FWIW, my '98 Pete 377 has a blend door controlled by a stepper motor. Check your circuit breakers and make sure none of the connectors behind the panel have been pulled loose.

edit: I may have misspoke, it's probably a servo motor - but electrical nonetheless.

 

Similar thing on my 2010 T660. Heater control valve blew up one night and leaked out all the coolant. The guys came out and hacksawed the copper elbow piece so it was now straight and put it back together. So now I had heat, just max heat no controlling it. Brought the truck and broken valve to shop for replacement. I drove that first summer with good A/C in the bunk but it pumped out 85 degrees A/C in the cab. My anxiety and bank account wouldn't let me put it back in the shop. Finally last summer the heater control valve busted in the bunk, I took it in and asked them to fix both. Turns out the shop never had fixed the cab valve after all, the tech said the A/C was indeed working, just the heater was on full max so here you have 38 degree A/C coming out blended with 138 degree heat.

Long story short, have the valve they 'fixed' looked at again.

 

Looks like this problem has hit my 2012 T660 as well. It's started off intermittently. Now cab only blows heat, bunk ac still operates. I'll have to give that heater core flow valve a look. Till then ugh, it's getting hot hot hot in this cab.