The temperature blend door seems to get lazy, perhaps from lack of use. I wanted some heat for the first time in years and didn't get any. I cycled the control several times and after the car warmed it came back to life. Give it a try if you haven't already. Maybe you'll get lucky.
Okay...hijack, I cycled through all the settings and still no heat. Cooling works GREAT! What is the next step/troubleshoot for a lazy mix door? (without taking apart the dash.